Well lately it seems like all pyrex is rare. Mostly since all the articles about how old pyrex is worth a lot of money. Htf things going for over double of what they would have 6 months ago.
If you do a search on ebay for “rare pyrex” you get a lot of results. Maybe 3 of the 2000+ results are actually rare. And you will know because of the bids or reserves on them.
If you are a newbie I highly suggest getting The Hot for Pyrex Guide to Rare and Hard to Find Vintage Pyrex.
Some things in this book that were rare are no longer rare.
Do your research to determine if your pieces are common, htf or rare.
Certain regions have produced more htf and rare patterns than others, mostly near old pyrex/corning plants.
I have been lucky to live fairly close to a pyrex plant. I have stumbled upon quite a few good pieces.
Below are some pieces I have found itw. And very cheap for what they were. The butter print mugs became an entire fiasco that I will probably talk about in a later post. There are only 20 known. I happened to get 5 at one time.
Check out @smokeyheightsvintage on Instagram to see all my finds.