Hm, that is very odd indeed. Occasionally I swear I've added things in before that I find later were never added, but I always assumed that maybe it was just an error on my part.
As pacpix has said, I don't recall Matt ever mentioning anything about losing information. We lost some stuff in the forums, but as far as the database and collections go, those were always backed up.
But yeah, that's not a bad idea about exporting your collection from time to time. That way, you can always double-check if any info does go missing. Items being merged or edited shouldn't affect the users who have that item in their collection...
In any case, thanks for mentioning it, ffmaniac2050! I always make the mistake of assuming someone's new when I haven't seen the name much in the forum. I should learn to check the profile page to see if they're actually new or not