Companies like to keep outdated trademarks, should the day come they want to use them again. When renewing Robocop trademarks, it was probably easier/simpler to rubber stamp everything else on the form.
Kinda like Star Trek TOS in syndication over the years (prior to Remastered). The prints ended with the animated Desilu logo and theme. Except it said (c) 1979 on it! Over ten years after they absorbed Desilu, Paramount went to the trouble to make a NEW Desilu tag with the recent renewal date. The reasons for these things are known only to pencil pushers...