It looks like those #'s stamped on the clips and buckles were some sort of in-plant use. I've seen some that looked like date codes, but other belts out of the same set can have a totally different style number. So, no, I don't.
Thanks! That's even earlier than I was expecting! What style are the front lap belts? I think they are dated 42F68.
I'd like some more data from other 69 cars to confirm the change, but the report appears wrong on that detail. A revision will be forthcoming soon.