The OA and RA numbers are the factory applied serial numbers, indicating the first fortnight of 1986 & 1989 reapectively. However, the latter ycle wears Shimano New 600Ex, which was only the 1986 & 1987 model years. A 1989 would have 600 Ultegra. Conseqently, I believe the RA is actually PA, representing 1987. This would make it another 912 but one model year newer.