I believe the only difference beside the nomenclature is that the A's have S/N.I think it is possible I have a P6302 rather than a A6302. How can you tell?
Here's part of the the MSR from July 10, 81
//Two current probes are now designated base items and have full product status, the A6302 (formerly P6302)
and the A6303 (formerly P6303). The purpose of this action is to identify these probes as commissionable
items and to allow the accumulation of statistical data. The effective date of this changeover is July 6, 1981.
Other than nomenclature the "A" versions are identical to the "P" versions. All of the advantages, are yours
(commissions) and ours (forecasts, targets, order history, etc).//