You have a very nice shotgun--I have an 1100 LT 20 Satin Finish because it looked nice, mounted very well and proved to be excellent to shoot. The difference is:
A Standard 1100 Remington 20 GA is a 20 ga barrel on an 12 GA frame and stock.
The LT20 is a scaled down reciever and stock. It has the same functional pieces but built to 20 GA scale.
The LT 20 replaced the Standard 20 GA more than a few years ago.