@User: Anything incremental related to extraction is much more difficult than for DRC, since the extraction results are in an external file. There is such a thing as incremental extraction but that's still a long way from running internal LVS, especially as the external results are still in .ext format and not SPICE, which implies that the netlist you want to compare against needs to be in .ext format as well. Otherwise, there's essentially no difference between that and running netgen. I tend to be distrustful of the incremental extraction, though. I have never tried to prove that it yields a valid result.