Sometimes they do tweak the mold after the 1st run due to feedback they get, but Innova will tweak a mold anytime so it's not just an issue with 1st runs.
Probably the 1st run thing is two things. You got one of them: Collectors. Back in the day there used to be cool 1st run stamps, and I have a few of those that I've hung on to just to collect. If you are going to collect golf discs, 1st runs are a logical thing to collect.
The second thing is plastic snobs. You know the guys...they only throw Rocs with the bird facing right. They only putt with a prototype Wizard. They will pull out a 1st run Gateway Inferno and tell you how the plastic was so much better on them than any later run and tell you they fly better than any later run and say "Too bad you didn't pick any up..." you know, plastic snobs. Plastic snobs love to fill their bags with plastic you can't get anymore, then try to work you on the course by telling you what a disadvantage you are at since he has all this great plastic you can't get. It's just a snob thing, last time I looked a 1st run Inferno didn't jump out of the bag and roll under the basket itself. You still have to throw the things.
So if somebody is trying to tell you that you HAVE to spend big $$$ on 1st run discs or you just won't be able to make your shots, they are just working you. There are hundreds of common discs on the market, and every shot under the Sun can be executed with them. A bag full of 1st run discs won't make you a better golfer. A poorer one, yes...but not a better one.