I use my lenses and don't get rid of them. I scratched the area that the coding shows when using the coding system, reapplied the pen and the black area remains no matter how many times the lens is taken off. So for the 75 dollars for the system, and a small file I already had, I have marked all my lenses and they show up just like I had spent 175 each.
M2 (got as NOS in 1974), M9, Biogon 25mm 2.8, 35 ASPH and 50 Summicron, 50 DR, 90 Elmarit (1st model), 90 Elmarit-M, 90 Summicron Pre ASPH, Elmar 135, Thumbs-Up (great finally my camera feels solid in my hand). Leica user since 1969 (IIIC 50 Summitar, still have)