I'd make that about 63-70 days in lamb, perfect timing for scanner to be most accurate. Having worked on multiple large farms, I've only ever seen an accuracy of around 99%, and mostly that is missing a lamb (ie quads scanned and called triplets, or triplets scanned and called twins, very rare to see twins where the scanner has missed one, I've even seen them mark down one live and one dead twin at scanning).
It's possible, but if your ram was taken out shortly after you saw them covered (ie they couldn't have been covered within a month of being scanned) I'd trust the scanner was correct.