No, I'm free to remember when we actually counted the houses about 18 months ago, someone stated the EXACT same bogus "600" number, and stated they did their counting the the EXACT same way you say you did.
If it wasn't you, then you must have an identical twin making the same erroneous statements as you at almost the exact same time you claim to have left UO. I see feathers and hear quacking.
By the way, I've never seen a dsfasfa house drop for any reason other than Silvani reducing one to a foundation (and it STILL didn't go away, it's just now a foundation, between Wind and Despise), and I catalogued mine by literally walking East/west strips, a screen wide, over the entire continent, coast to coast (or coast to mountain, then doing the same strip on the other side of the range - if I ran into a river, I teleported across it) then exploring the passes, islands and peninsulas that weren't doable by such strips.
Such numbers were counted by several people, with redundant checks, and each ended up with a quarter of the houses for the whole continent, you claim for 1/3 (granted, most of them ARE concentrated on the top 1/3 of the continent), within a variation of about 1-5 per person (which were resolved by T'Amon checking the lists against each other).
You sure you weren't counting all the houses in Trammel - or had multiple markers for every house? (UOAM doesn't replace one marker with another, after all, it just keeps stacking one on top the other if they are for the same location - I found that out entering SOS for a fishing trip).