I surveyed most of a township in one state along the south line of the state back in 2001, using CORS reductions for the control, then RTK to locate most of the corners, some static also. Then set on an old NAD 27 first order NGS monument in a township to the south of the state line and survey most of that township from a CORS reduction.
I tie the monuments along the state line and they are about 0.05' different from the new control. NICE!!
I was worried cause the NGS NAD83 numbers on the datasheet for the NAD27 first order point differed from my CORS numbers about 6'. Oh well, I can't be wrong so the datasheet is off more than I expected. But it is nice to see that you can use the CORS data base to tie into older GPS control and be that close, particularly when the surveys are so large.