Is it correct, then, that one would need to memorize all 70 moves in order to get quicker on the LL so that they can get away from using the R'D'RD method?
The group of 70 algorithms is for a 2 look last layer. For instance, you look at the last layer once, and then orient the corners AND edges with an alg. Then you look at it again, and then permute the corners AND edges with a second alg.
Many people use a 3 or a 4 look last layer.
The 3 and 4 look last layers use specific algs taken from the list of 70.
For a true 4 look(where you Don't repeat any algs), you would need:
3 that flip edges:
straight line across - F (RU R'U') F'
little "L" - F (RU R'U')(RU R'U') F'
no edges correct - LFR (U2 R')(U2 R)(U2 R'F'L')
7 that twist corners (sune, antisune, double sune, the cross "on heel", 2 to one side, 2 to opposite sides, figure 8)
Sune - R U R' U R U2 R'
Antisune - R U2 R' U' R U' R'
Double Sune - R U R' U R U' R' U R U2 R'
Cross on heel - R U2 R2 U' R2 U' R2 U2 R
2 to one side - F2D'FU2F'DFU2F
2 to opposite - R'F'LFRF'L'F
figure 8 - R'F'L'FRF'LF
4 for permuting edges (M' means the vertical slice in the front goes UP):
switch across -M2 U' M2 U2 M2 U' M2
switch adjacent - R B' R' B F R' B' F R' B R F2 U
3 cycle CW - F2 U M' U2 M U F2
3 cycle CW - F2 U' M' U2 M U' F2
3 for permuting corners
3 cycle CW - R' F R' B2 R F' R' B2 R2
3 cycle CCW - R2 B2 R F R' B2 R F' R
Adjacent swap (I honestly just do 3cycle CCW, turn cube Counter clockwise, 3 cycle CCW)
For a grand total of 17 algs. (well, really 16 the way I did it)
To figure out what you're actually looking for, just do the alg over and over till it solves itself. Whatever it looked like before it was solved is what you're looking for.