There are several different kinds of labels for all "legit" roms too.. Back in the mid 90s there were probably some ESCOM burned 3.1 chips available, but nowadays, who knows. There have been no mask rom 3.1 chips to my knowledge, only burned ones. Some with a window under the sticker, some windowless.
Have you noticed how there's a neverending supply of ROM chips for each model still in every dealer's catalogue?
I'm pretty sure each dealer just burns them on demand and then pays Amigainc some royalties for them.. At least the idealist in me believes they pay. :-)