mine had a white label on the inside of each flare with that number on it. i also think i might have seen it kind of scratched into the inside of the flare. i had the same problem with my fenders. they changed the style of them but they were only going to send me new ones for the 2 that were broken. i just kept calling until eventually they gave in and sent me a whole new set. hopefully you'll find it.
Actually the ones I bought were factory "blems". Which meant there was a small defect some where on them. I payed $139 and the blem turned out to be the side reflector hole was in the wrong place, so I redrilled them. I think you can still get them for $199.
Those look like the flares that were on my jeep when I bought it. They had the same problem you describe, very brittle and cracking all over....I wonder if they werent a cheap knock-off of bushwacker flares....otherwise maybe its dryrot and thats to be expected? Anyway I replaced mine with Warn flares and love them - much heavier and feel a lot more solid.
It's probably a little more detailed than that. They are gonna need a "batch" number for a number of reasons.
1. If there has been a recorded "Quality Control" issue with that batch they are more apt to send out a free replacement.
2. Designs are constantly changing and if they send you one based on someone else's batch number you are likely to get a replacement that doesn't match what you have. And if you're only replacing one or more, you'll be right back here complaining how they sent you the wrong one.
3. There are tons of companies out there making "look-a-likes" and they want to make sure they are replacing theirs.
So, my only advise is to man up, get out there and remove one of the flairs, get the number and go from there!
Take the caps off and spray some good penetrating oil on them. Let it soak for a while and proceed with the removal. Make sure you the correct size Phillips bit and apply pressure.
Relax man, I have been waiting for my tube fenders for a month and they have not even been shipped yet. My jeep is fender less, so all can do is wait. I can't drive it without them and my old ones are trashed.
Oh and by the way, when you do get the old flares off. Replace the Phillips head screws with something like Allen or Torx head screws. You will like that more in the future.