This is just saying there were these models designated as A-bodies before GM changed the letter to G in 1982. (These models were A bodies going way back) Why the change? I don't know. The part number book will say 78-81 A and 82-87 G, same part.
I can tell Wiki isn't a great source for this.....it only lists the more sports image models.....for instance the Olds 442,instead of Olds Cutlass. It would have been more accurate to be all-inclusive....Malibu, Monte Carlo, Lemans, GrandAm, Grand Prix, Regal, Cutlass.
And why did they leave off the Monte SS, the GrandAm, the Grand Prix SJ, and the Regal?