[69L72RS]

The date difference is fine as long as the gears are a mated (lapped) pair/set.

When the gears were made, they were produced in equal order quantities. I'll use 100 for the example, as it was explained to me.
The gear plant created an orders for 100 pinions and 100 rings.
During production one more of the ring gears got damaged/scrapped. So there would be extra pinions.
The extra pinions sit in surplus until:
1) An extra ring becomes available from a later production run, do to damaged pinions, to allow a set to be paired/lapped.
2) Enough of them piled up justify a balancing order quantity to be produced.

I was told that the r&p sets only left production as paired/lapped sets.

I have several NOS and used sets that are mixed dates. I think the largest spacing I have is from 11 67 to 5 68 for a 3917971 r&p set.
Hope this helps.
Eric