As far back as I can recall, the DC area lots have marked the cars. back in the 70's or 80's when I lost my ticket, the cashier went to the back of my car and pulled a little rolled up ticket with the date of my first overnight in the lot.

on my last couple of lost tickets(get old, already) they punch up the lisence number on the device in the booth, and get the time of arrival.

I have a feeling this happens with a significient percentage of the patrons.

at BWI private lot last week, I was stuck behind someone for about 15 minutes while he turned the car upsidedown. Seems he could not find his voucher for 2 weeks of prepaid parking. no discount for prepaid. must have voucher. sounds like a bad option to me.