I think it is the nature of the business now of so much being done away from Hollywood plus independent companies actually shooting the productions. But, I have also seen that when a TV show is shot at Universal, Paramount, FOX and WB, where they are on the same ground for the last 80 years, when they need an antique piece, it is usually something from classic films still sitting in the warehouse. One piece I have from RKO, from the 30s, is in Brando's last film done in 2002. A clock from THE ADDAMS FAMILY TV show was in a late 90s FRASIER episode. Other pieces were used in ST:TNG.
I realize they are the exceptions, but all are marked from their respective studios. Once, the majors embraced TV in the 1950s, things were reused over and over again.
Today, they use stickers with bar codes, as with any business, valuing assets is required for taxes and other purposes.
rick