Thanks Cinders, that made a difference, your '21 was showing up as an anomalie without the correct date.
Your '16 puts it in the H category....is that correct? it would have been selected for conversion in the second run of H rifles,
and your '45 could be a FTR from the 58/59 batch of 2,949......if it is stamped FTR, otherwise a club rebarrel job.