Allow me to add one more theory as to the lack of a bonus round category display...
Unless someone can document that they were using an actual Chyron character generator, I'd guess (based primarily on the style, size and proportion of typeface) that they were using an earlier non-Chyron/non-Dubner model of CG. If I had to guess, it looks almost identical to the model we used in my first video production course in college, which was held in 1992 in the "old" studio where all the ancient equipment went to die; I've been sitting here for 15 minutes googling and racking my brains trying to remember what the name of that CG was, but I can't think of it. (I do remember the shock of having to use this crappy thing when I'm used to using the student TV station's Video Toaster, with its multiple colors and four--count 'em, FOUR!--fonts.)
What I definitely do recall about it, though, was, unlike today's CG's which can store thousands upon thousands of graphics as files on a hard drive, this one only had four pages of storage in RAM. You had room for four graphics for instant recall. Allow me to advance the theory that NBC perhaps had the same unit, or one similarly equipped, but had five pages of CG to air during the credits sequence. The last four pages (let's say Susan's wardrobe credit, Chuck's wardrobe, "the show has been edited" or "contestants have been provided the rules" and/or a copyright page) could be stored internally and recalled into the on-air buffer live, but the first page in sequence would have to be manually typed into the on-air buffer. And if memory serves, the first page would likely have been the long list of companies which had provided prizes. Perhaps given the choice between stopping production for five minutes while the CG op typed all this in, or just skipping the category name in the bonus round and letting the CG op type it all in during that time...
Like I said, just a theory.