Here's my impression, and a few facts.
There is, and was at the time, a federal list of items for anything related to government purchased parts (remember, anything, all the way to toilet seats). I have the gov't spec on the 55J14 G-1 jacket, and every single part of the jacket has a gov't number, or a Navy number, or both. Even the stitching type has a gov't number. I'm not joking. A lock stitch is given a number like V22-LS-1448. And a diagram comes in a massive binder with graphics of every stitch design, and the machine to do it with and the thread type (numbered and described) and the official gov't number of stitches per inch.
So, any part going into any item bought by the gov't has a spec number, design, and dimensions. For the A-2 jackets, the knits would have a fed or AAF number, and then a diagram that shows the type of wool, the exact number of wales per inch, the exact number of courses per inch, and the exact size of height and width of the waistband, the cuffs, how to cut them, what each different jacket size would require, etc...
To make any of these items, one has to pitch for the contract. Yes, that means Talon, knit makers, snap makers, cotton lining makers, thread makers, and even jacket makers all had to bid on a contract. The winning bidder would receive their federal or AAF spec sheet and produce the item needed for the contract, under contract, and would have to have their item inspected by an AAF or federal inspector.
Even the leather had very tight specs. It had to be a certain grade, and certain thickness. I spoke with Mituhito Aota (author of Full Gear) in person, and though he didn't have it on hand, he owns both the Fed spec and AAF spec for leather during WWII, which gave a certain range of thickness and type of finish for leather used in flight garments.
So, the point is, do you think any company making jackets would be trusted to "find" the right parts according to a federal or AAF spec sheet, if that spec sheet had to be adhered to, for the right price, from a company that was trusted by the gov't, and delivered on time? No. The AAF covered it's own ass by purchasing all the parts. No officers got in trouble if they did all the right bidding and purchasing. Companies could get in trouble, but not the officers managing the deals (but I bet there was corruption to some degree).
Now, for the Aero knits. The world was much smaller at this time, and I'm guessing that some of the contract material was done on a more local scale. So, a company like Aero would win a bid for jackets. The officer would look for New York area parts as much as possible, and I would guess that there were a number of knitting mills in the New York area. Find a few, let them bid, and the winning bidder did the work. They screw up the color (massively...it was the "wrong" color by all counts), and the officer decides, with that volume, that it's not worth it to do a second run, as they would loose time on delivery. They scold the company and maybe even take a lower price per unit, but take them.
I'm not saying that happened, but in the pressure they were under, it could have happened that way. Obviously, when it comes to leather color, A-2 jackets are all over the place, from light brown to almost black. The leather wasn't rejected, but I'm sure a few officers were disappointed with the colors chosen. But would they reject leather in hand? No. Just use it.
In the 1940s, in the USA, there were many tanneries in each city. So, I would venture to guess that some contracts were fulfilled through several tanneries, not just one. For Aero, they may have had 1-5 tanneries making the hides for the 21996 contract, as an example. We see one that's russet, and another that's seal, and wonder what on Earth happened. Simple - different color managers at the tannery had differing ideas of what brown should be. Every tannery had different chemicals and methods of tanning (just like chicken can be cooked in every different manner imaginable), so the leather from one tannery would be stiff and grainy, and another tannery would have thin and flat leather.
Same with the linings - some companies used tan, others a dry dirt color, and others dull orange. Was any color wrong? Probably not, but they sure were different. Lowest bidder does the work.
I have USN knits from WWII, probably replacement units, and even the knits came in a box with the contract number, date, contractor, and other federal numbers on it. The zippers had very strict federal design specs - no jacket maker would be trusted to find that stuff on their own. It's the same way today with military purchasing, and it keeps the buyer safe in getting what they asked for (except for those red knits).
That's why the price per jacket only covers the company assembling the jackets, not the parts.
Also, Charles DiSipio posted a number of contract details years ago on an older forum, and one covered a 1935 request for A-2 jackets. The spec for the lining was cotton, not silk, so by that point, cotton was the demanded material. And some of the papers he found covered tanneries asking to bid on cowhide leather for aviator jackets. One of the failed bidders for an A-2 contract was Ideal Sportswear, and the process was that they would submit their bid, and be given a jacket from the AAC to make a test copy of. This may explain why some jacket maker designs are similar to others. A crude drawing was giving of the jacket design, but a physical jacket would be sent to copy. Maybe Perry got a Werber or a Rough Wear, or Dubow got an earlier Aero - who knows, but each company would get a chance to make one copy.
I hope that helps.
John