Found the answer to my first question:
"Regarding Site NAC Operation:
You can select (use or ignore) Site NAC of P25 Trunked Systems (including P25 OFT) in RRDB and Favorites Lists. When we added NAC support, we did not anticipate that the NAC would be incorrect in RRDB for many sites. This has caused many reports that the scanner stopped working with the new firmware (it was actually working correctly and rejecting the site traffic with the "incorrect" NAC). So, we've added an option to ignore the programmed NAC."
It's been discussed somewhere and I had a chance to see this, if you program a NAC and it's not correct or you have other site frequencies programmed in, the "corrected" NAC will flash alongside the "programmed" NAC.
Last night one of my sites briefly went off line. Under my site frequencies section, I have other site's frequencies programmed in the event I'm out and I lose the control channel. Under the previous firmware, this would not work as the NAC site was programmed. With the latest firmware the SDS 100, immediately picked up a neighboring sites control channel and the new NAC was flashing in the display. Didn't realize this until I noticed some choppiness in the transmission and took a look at the display.
I have set mine to Display NAC, but I don't use location control or Zip code based programming from RRDB. Instead I program using the database as a tool and unless I put in the CTCSS,DCS or NAC codes myself, they are always set to Search until I can confirm or another local user emails me or texts me that he confirmed the entry. This could be a reason why I've had much success with my SDS 100, while others are reporting programming issues?