If you get to the show on time you should have no problems getting in. The only time where there could be an issue is if you show up midway through the show and venue is at capacity.
This is generally correct. However, I'm not sure of the last time Nightgrass tix were in such high demand.
If you want to get into YMSB on Friday, I'd be there EARLY. If you want in for Emmitt-Nershi, I'd be there on time.
Even if you get there and a show is at capacity, they will start doing a 1in/1out policy...or should at least. (meaning when someone walks out of the venue, someone gets to go in).
D.