The original or “A market” 777 variants were the 777-200, 777-300, and 777-200ER. The 777-300 was a stretch of the 777-200 and the ER was a long range version of the 777-200.
The 777-200LR, 777-200F, and 777-300ER were the “B market” 777 variants and were essentially an NG version of the original 777, similar to the relationship between the 737 Classic and 737NG. They featured more powerful and more efficient engines, aerodynamic improvements, improved tech, and a MTOW increase. The 777-200LR was the base model, with the 777-300ER being a stretch and the F model being the freighter version of the 200LR.
Think of it as 2 separate aircraft families in that sense, the Classic 777 and the revamped 777NG family.