I had a Sporter II rifle that I bought brand new in 1985, sorry I had no record of my serial number, mine had an upper receiver with teardrop forward assist and no case deflector.
SP2 series were made from around 1982 up to 1989, in 1988 they were replaced by the model R6550 AR-15A2 Gov't model rifle.
The SP2 rifles changed upper receivers during their production run, the first early version had no shell deflector and no forward assist just like the older SP1 rifles.
The second version was like mine with the addition of the forward assist.
Third version is like yours with the improved upper C7 type with shell deflector and forward assist (round button).
The last late version the upper are A2 type with adjustable elevation rear sight, shell deflector and forward assist.
I had seen the serial range number of the SP2 series, and other newer models listed on the book Black Rifle II, The M16 Into the 21st Century (2004) by Christopher R. Bartocci, but I don't have this book, they're available at Amazon and bookstores.