Curiously enough, I expected a replacement tank I got from Jbugs to be coated inside. Like you say, that’s what is usually said about them.
There was a note saying it was sent without that coating, and yet their web page has a prominent warning about the coating needing to be cleaned out.
https://www.jbugs.com/product/113201075AB.html
Wish I could locate the note it had upon delivery. Something about the manufacturer no longer used that coating. It only had foil seals (were not airtight either) on the filler and fuel sender openings.
Wish I could say with 100% certainty. I still haven’t installed that tank, or cut and welded the filler neck. Just took a look inside again and I see nothing that would indicate a special coating, looks like bare metal to me. Don’t know why I didn’t leave that note with the tank (stored indoors), but I sure remember about that note saying it lacked the coating because it surprised me.
Maybe it was a California thing…? Jbugs is located there. I’ve just now asked about it on their web page for the 1961-67 tank using the Q&A. Hopefully a reply will show up.