It's rather inconsistent. For example, I visited a thread right before this that I had read before, and it went straight to the correct post. Visited this thread, and I got sent to the same post I read 2 hours ago. The URL was:
https://www.chiefdelphi.com/forums/s...83#post1633383
This URL appears to be pointing to the post I was taken to (post #24) instead of the post I should have been taken to, post #25. I know, it's a small difference... but on longer threads that ends up being pages of posts different.
I'm not sure how the site stores the most recent post read, but I'm guessing that would be a good starting point, as the link itself doesn't seem to be generated to point to the correct post.