The Invector Choke system was first introduced in 1983 and only available on Citori, BPS, and BT-99 models. Fixed choke barrels were still available as well. Please note that the Citori Lightning model wasn't introduced until 1988. All Citori Lightning models in 12, 16, and 20ga. were only available with the invector choke system (and still are). 28ga Lightning Citori's were still fixed choke only.
From 88 to 99 will interchange.
99% of it will interchange.
Yes
Call Browning with the serial number.
95-99
No
Call Browning with the serial number.
nono
96 to 00
The 2 letters PP in your serial number sequence indicate that your Browning BT-99 was made in the year 1988.
1978