Thanks Del! So they did continue the serializing well past the 1975 notation I found. I really have not surveyed the NIB 897UH to see when they changed the stamps leaving off stainless. I suppose it might have been when they started using the "+".
I'm not aware that having the serial number or not affects the value one way or the other. In fact, few people even recognized that some had it before I pointed it out, though it may well have also been posted some time in the past. It micht be an indicator that a knife was produced before ___ date, if we knew that date. Otherwise, it is just an interesting factoid at this juncture, like the date hallmarks on the butts of the Benchmade '49ers.
Michael