In fairness it took me a while to also put 2+2 together to realize that in those situations it's a pretty logical deduction that they changed the prefix during that year but don't show the last s/n of the old sequence, only the last one of the new sequence, so an s/n can "fall into that crack".Fred,
First, welcome to LTG!
As I gather you noticed, the SN of your DV-52 is higher than the last reported number for 1993, but doesn't use the AD52 prefix that came into use in 1994... the SN lists just aren't complete.