1971
Incomplete serial number. Get the complete number, go to Browning's site, Support, Date Your Firearm. They have a complete listing.
If you go to browning,s home page there is a way to age your shotgun there.
You must call Browning as the sn you gave does not follow normal convention.
2003
1988
BT99
Please add the serial, but it is likely a single barrel trap gun such as the BT99
Believe that your serial number is incorrect. There are no BT99 serial numbers that start with 47. There are however serial numbers that begin with 74 which is the year (1974)that they were made.
Japan
Your gun was manufactured in 1993 according to the serial number. They are well made highly sough after shotguns usually valuing between $1500 and $2000 depending on condition.
100-1000 usd