I explored this issue a little in 2011 ( I can't remember why ) even though I had a full printout of my FLSH when i bought the car personally from the Parts Manager at Lexus Poole. I guess he had obtained the computer records easily at that time.
NOW, if my memory serves me well, the records were kept centrally on the computer at Lexus HQ in the UK somewhere at that time. The local Dealer was just the conduit for getting the data.
How and if they keep that data for a 20 year old car, well, who would know !
Malc