The 2 letters PP in your serial number sequence indicate that your Browning BT-99 was made in the year 1988.
Call Browning with the serial number.
1987
1971
Go to Browning's site, click on Support then date your firearm.
No
Ask again and include the serial or go to the link below.
No
1978
69
Right
Browning.com has sn data under customer service.