netlist debugging is almost impossible. however, since the ADD has an regular stucture, the following things might be help:
1. identify the stucture, BK, CLA, CS, RIPPLE... it's very crucial, for each of them is bulid on different equations.
2. identify the critical signals, llike Pi, Gi, in BK structure. And maybe u can do it down from CO.
3. partition the netlist into blocks, base on the Critical signals.
after that you can have a structured, block based, ADD.
Anyway, it's very time consuming, try them on the 4 bit adder first to get to familiar.
good luck