When I started the quest to organize and build my old LEGO sets there were certain sets that I absolutely remembered having. No need to go through catalogues and compare my part inventory to figure out what I might have owned back then.
Now that most of those sets are being built, or at least the pieces have been set aside I have started to figure out the rest of the sets in the lot. Many of them are newer ones from my kids, but there are still sets that are from my era. Sets that I don't remember owning. They must be mine as they are from early nineties, long discontinued at the time my kids were old enough to have LEGO sets bought for them.
The mystery sets are all from that later time period. There might still be some smaller sets from the earlier I missed. From the later sets I only remembered owning a few. There weren't that many from those years as it was the beginning of my LEGO "dark ages".
It's interesting that I can so vividly remember those older sets, but have no recollection of the sets I owned ten years later.