Last I heard, there were two Pyrex’s in production, and you could tell the good from the bad by subtle differences in branding.

Edit to add: https://lifehacker.com/that-viral-pyrex-brand-hack-is-horseshit-folks-1850157381

So, how can you actually tell if you’re dealing with “real” Pyrex? As a rule of thumb, it’s safe to simply assume you aren’t—at least, not if you’re in the United States. The “real stuff” hasn’t existed at all in the U.S. market for at least 30 years. Pyrex started phasing out borosilicate glass in the 1950s and had stopped using it entirely by 1998, when World Kitchen (now Corelle Brands) bought the license to the PYREX and pyrex brands. Unless you buy your cookware from a vintage shop that can prove it was manufactured in the 1940s or earlier, you’re very unlikely to come across borosilicate glass pyrex.