My daughters are built like you. One of them had bust surgery and went from an A to a C cup. Since most garments are made for B cups, now I'm doing full bust adjustments on her garments.
The few Junior patterns that are out there will fit you a little better (Junior sizes are made for the developing figure). Butterick and Vogue will also fit you MUCH better than Simplicity and McCalls which really are patterned for a more "mature" rounded figure. (By the way, congratulations on your youthful figure).
To help explain how to make a reduction to the bustline it might help to explain how to make an enlargement. In a full bust alteration you slash at the PATTERN's natural bustline, up and down at each bust point and across...and you pivot everything if it is princess line; if it is a garment with darts, you spread the darts until the garment hangs straight and then you come back to within 1 inch of the bust and start the dart back to the seamline. The extra width of the opening goes into the dart until it is the side seam "fits" the original seam length.
So....you say, "What does that have to do with MY problem?" Well, to make the bustline smaller, you just reverse the process. You pleat the garment on the bust line and take out the fullness, then adjust the dart down to fit the seamline. The tip of the dart ends up coming to one inch from the bust point and tapers to the seamline.
Go down to Wal Mart or to Hancocks and buy some stable fabric from the sale table and make up a particial garment..just from the shoulders to the waist of your pattern (actually a plaid or a gingham check is best). Then pin your "mock pattern" so that you can check your fitting. After a couple of these you'll know exactly what to do to get the right sizing and fit on your patterns. By the way, when I do that, I do go ahead and do a contrasting stitch around the arm holes and neck so that I can see how the seams will be effected. I baste everthing, including darts so that I can rip or tear if I need to move them. Just have fun with it! You'll be making lovely custom fit garments in no time!!!
The purpose of dressmaker scissors is to help keep the fabric as close to the table as possible when cutting. The bent handle and angled tip allow you to operate from an elevated posiition while cutting while the scissors rest on the tabe. Although there is a slight lift, it should be minimal. (I love the "sing" of the scissors as they cut, if you are cutting properly, they should make that noise). Any lift of the fabric from the table almost automatically allows the bottom layer to be larger than the top (amount depending upon how the fabric is held (rolled or straight). This can probably explain why (sometimes) garment pieces don't line up properly when sewing, esp. in stretchy fabrics or fabrics that creep. Also, the more layers you cut, the more the differences.
Many people are choosing to use rotary cutters when cutting their fabirc. I find that expensive and I don't have much control without using a guide. However, if you can develop this skill I think that it is probably much more accurate as there is absolutely no lift.
I haven't tried the laser scissors so I've got to ask, "If the laser penetrates all types of fabric, what does it do to the surface below?" The cutting method I have seen in industry was like a saw. They layer what seems like hundreds of layers and cut with a saw penetration from above.
Back in the mid 1960's patterns were smaller and shaped different from RTW. The two industries decided to create a sizing standard, which they did, making all patterns and RTW sizing exactly the same. It was called NEW SIZING and IT WORKED...for about a year or so. The differences started when the "finer" dress stores started handling slightly larger garments in RTW for their designer lines. Within a few short years, everyone down to K-Mart had their designer lines and the "finer" stores had to still have larger vanity sizes in their designer lines...because after all, everyone knows that designer clothing runs larger.
Well, the net result is that the home sewing industry is still obeying the rules while the RTW side is all over the place in sizing.
The first thing you have to do is stop thinking about sizing as universal...it is not. Pattern sizes are pattern sizes, they are no longer the same as RTW. Also, when we fit RTW garments, we fit them by the way we want them to look. In so doing, we often use the RTW ease as part of the garment's fit, what was intended to fit loosely, often is purchased in a smaller size and fits tightly, while we brag that WOW, I just bought a dress two sizes smaller! The mfg. would say WOW, they just bought a dress two sizes too small. To compensate, several of the pattern companies are playing with their sizing with disasterous results but they are also starting to put two types of measurments on the envelope: the body measurments AND the finished measurments. Although all patterns are intended to be purchased by the body measurments and the ease is determined by the type of garment, fitted, semi fitting, loose, very loose, most people will learn to make all patterns (with experience) in the manner they expect them to look. There are charts avail to show how many inches of ease in each of the major body parts constitute each catagory of fit in the major types of garment (skirt, pants, blouse, etc.) and if you read the directions, the pattern mgf will tell you the fit of that garment.
As for pattern to RTW ratio? In sewing professionally, I've found the smaller the person, the more sizes (up) the pattern has to be. I've often had a person who told me they were a size 3 actually wear a size 8 or 10 pattern by size. The differences between the smaller sizes are closer together in measurments too. By the time you get to a size 14 pattern (or so), the differences are less between RTW and patterns.
If you will notice, they recommend the garment for an hour glass or inverted pyramid figure. Vogue is very good about giving you pointers on what figures will look best. They usually only make a garment up to the size that they think will be flattered by their pattern. That is why sometimes pattern sizes stop "early". I think you'll be safe in this garment.
I agree that it is a flared skirt but I think that the whole piece was cut on the true bias. I can't tell that it has a seam in the front (some do). To get that kind of drape it almost has to be cut on the bias. If it has a seam it proably has a little more fullness in the front as well as the side seams. Looking at the top of the dress, I can't tell if there is a seam going through the bust line or if there is just a stress mark on the garment (from the way she is standing). If there is a seam, it like a modified princess line that appears to stop somewhere in the area of the waistline, although it could easily be bias cut also and extend to the hemline which could explain what appears to be extra fullness in the garment. The color does not lend itself to clear detail. If there is not a seam there, then the dart has been pivoted to the top of the garment as I don't see a dart either. It is a cute dress and a real retro look! Very flattering!
I always buy for the bust. There is just so much to altering busts and shoulders. The waist and hips are nothing compared to that. In some patterns the waist is a close measurment (really does depend on the pattern), in others it isn't even a problem. In your case, buy for the small, and enlarge the waist if necessary. There will be ease in the pattern but you can't always use that for part of your body measurment. In close fitting garments that can be a big mistake. As stacysews stated, you can always cut between the lines if the pattern is multiple sized...that's why they now print multiple sizes on the patterns in most cases.
THe new patterns are pretty easy to resize. Just lay out the pattern and redraw it. Decide how many sizes up or down you need to change the pattern. Then, using the lines on the pattern, in this case, it is probably a 14-16-18 pattern and you needed a 20-22-24 pattern, so...set a seams gauge on the size 16 line. measure to the size 18 line, move your gauge over to the edge of the size 18 line and draw a mark on your paper. Do this all over the pattern, down the sides, across the front (where needed), etc. Your new pattern should match the grading of a size 22. There will be sections where you'll be able to just take a yardstick and increase the line, however, there will be places like corners and crotches (in other patterns, necklines, shoulders and arm holes) where you'll need to pay particular attention to the lines and they will be much different. There will be some places, like the top side of the skirt where the amount will drop considerably, even be less than the original line and extend. You can do the same basic thing if you needed a size 22 waist but a size 16 hip.