On most commercially-made P53s, the date appeared above TOWER (Birmingham guns - the date did not normally appear on London P53 lockplates). This was following British regulation military use. However, for those that show TOWER over the date, this appears to have been just preference of the lockplate engraver or perhaps the lock maker. I have seen no pattern in this in original P53s.
As far as either being more desirable for collectors, I don't think there's a difference.