I think what may clear this up is, Remington overran their serial number range on both the 1903A3's and A4's. Remington placed a "Z" on the Remington A3's and A4's that over ran the s/n base. Smith Corona placed a "C" on their A3's. So a Z marked Remington is not always an A4. You need to know the s/n block for the A4 which is Z4,000,000 to Z4,002,290. Only this block of Z prefix are A4's. All other Z prefix Remington's are A3's.