Payment number recycled

When we enter manual payment with voucher match P0413M in e1 9.1 and let system assign the payment number for PN type, we notice that the system sometimes would look for an previous voided PT number to assign to new PN payment. Here's how its working, here's an example:

Payment #84646 doc type PN was assigned based on voided PT 84646 number from a year back. The next number 84647 was preexisting number so it skipped that number. When we finally get to payment number 84731, there was another void of PT payment so system assigned 84731 PN as next manual payment.

Is this normal for system to find an old voided number and assign this to new payment? Here's what I find on the knowledge material.