When searching for my own posts, it only went back 500 posts. Is that normal? I thought all my posts were preserved and searchable. If not, is there a different way to search (I found a post and clicked on my own name and selected “Find all posts by…”)?
Not sure if I have the answer but wasn’t there some “Winter of Missed Content” that posters bring up sometimes, not sure what year it happened but I think a lot of threads and posts were lost and never recovered during said time period?
When I search anyone’s post history it only comes up with 500 posts, so I don’t think that’s it.
Yes, that’s normal. It’s always capped at 500 posts.
You can do an advanced search and search for threads that someone posted in, and can select 1 year ago and older, 2 years ago and older, etc. to go back through all of the threads.
There’s the Fortune 500, the Daytona 500, The HTTP Status Code 500 (appropriate here!), the S&P 500, the Indianapolis 500, and now the SDMB 500.
So don’t be greedy! 
You can also show results “In Ascending Order” to get your earliest posts from the beginning, and you can also search forum by forum. The OP has few enough posts that that might find all of them.
The Winter of Our Missed Content was from December 7, 2001 to March 10, 2002. Posts made on the board between December 7 and February 11 were lost. Between February 11 and March 10 a temporary board was in service elsewhere.
Since this precedes the OP’s registration it has no effect on his post count.