I would treat the dates as a rough guide anyway, and not get too hung up on them. Kits get bought and then occasionally might be ten years in the completion, so you can have a 2003 car with a 2003 chassis and body, or a 1993 chassis and body. Or you can have a 1989 car that someone has retrofitted with a 2001 body etc.
If there is something in particular that is important to you, you just need to learn how to recognise it; don't forget, two or three sellers down the line the current owner may be blissfully unaware that their pride and joy is actually a hybrid of different years parts.
On the Ford parts question, again, I wouldn't read as much into it as their sometimes appears. Yes there may seem to be parts made for lots of Ford options going back years, but that doesn't mean it's anything like OEM quality still. (Though there are plenty of fine quality retro parts). There's a lot of nasty Chinese re pro stuff as well as just mediocre quality stuff. A classic example is some of the replacement gear sets for the Sierra diffs, the quality just isn't the same as the OEM Ford parts, as a consequence makers have started to move away - Caterham had loads of issues a few years ago with diff noise.
The Mazda market is huge and global. It's not going to go quietly!