I am a late comer to 2E. I was in the middle of the Mummy's Mask AP and decided to wait to jump into 2e. I am having confusion as to which version of books I want to buy. As I understand there are up to three versions of 2E products available. Please correct any misconceptions I have.
2E............Original content released under the OGL
Remastered....New re-released content released under the ORC.
Special Edition...??? Is this remastered?
Special editions are just fancy covers.
Special Editions are special covers of the same book (nothing is changed inside), so you'll need to look at the book title itself to determine if it's legacy or remaster.
Yeah, the Special Edition covers appear on both the Legacy and Remaster products.
It may also be worth noting that 95% of Legacy content is still compatible with Remaster games.
It's good general advice to suggest you purchase the most recent version if multiple exist.
That aside, if you are running APs and not homebrewing a campaign, I don't think you should worry about it too much.
Using *just* Archives of Nethys can be a bit tricky as a GM, so you may want the core books. If you have a pdf of the GM & Player Core books, you can keep them open to both ctrl-f search and then flip pages from there.
My recommendation is you instead buy whatever odd books catch your fancy, which signals to Paizo that you liked it.
Archives o N (and the wiki) are great due to linking you to the source books. While the rules / mechanics are extracted for the needed public use, you can get neat extra nuggets and context if you buy the book directly.
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To rephrase and summarize, (if you run APs) I suggest spending the barest minimum on the core books, and if you fancy it, you can splash some cash on weird/old books that catch your interest.
It's worth pointing out that the only remaster products to share names with their legacy counterparts that have been released so far are accessories (The GM Screen and Spell Cards) and the beginner box. This will change in the future since the next printing of Guns and Gears will be under the ORC, but we still don't have an ETA for that annd Guns and Gears goes through print runs a lot faster than most of the non-Core line, so further remasters.
The only non-core book being supplanted is Lost Omens: Gods and Magic, which is out of date as much due to lore events as any mechanical changes. November's Lost Omens: Divine Mysteries will cover what was in the old book, updated to account for the numerous dead gods and newly ascended divinities.