Not sure if I can help directly, but I'll attempt to fill in some info gaps here . . .
Your first link/pic is that of a 3" bbl Smith 686+. I have one, right down to the SKU. A fine gun. My carry gun in the cool months when I can layer up a bit. But I digress. I bought mine factory new and its grips don't cover the backstrap. I agree that the illustration rather appears that they may cover the backstrap, but in reality, they don't.
Your second link/pic is that of a K-frame model 66. That pic - an actual pic and not an illustration - shows with a good deal of certainty that the grip covers the backstrap. I have a K-frame model 67 and its stock grips cover the backstrap; however, they are also "conversion grips," which convert a round but to a square butt, so to speak. So my grips and that model 66's grips are apples n oranges.
I'm curious why you want grips that cover the backstrap? My L-frame handles great with its stock grips. My hands are small. Maybe you want a little more reach to the trigger than me??