It only takes a few years for mother nature to "restore" a dug shelter. It's very hard to determine as some diggers start at the front and go to the back....this style of digging/sifting normally results in the debitage located in the front (e.g., the wall sand is sifted and dumped at the front of the shelter). We call this reverse back filling. Others dig from back to front which results in the debitage from the front being deposited in the rear...true back filling.
In my experience, the largest concentration of artifacts will be against the back wall and that's where I always start, I want immediate results...this helps me mentally when I run into an 8 hour dig with nothing to show.
I always key in on the "knapping" rock. Most knapping was done sitting down or at least supported by some structure...the process of knapping requires leverage that is difficult to achieve standing up or sitting directly on the ground.
If your site has a "number" with no associated record, it was probably ID'd as a site for excavation. Test digs or lack of funding may have eliminated the site from exploration. A test dig sometimes means that nothing was found but more often than not, it means that the condition of the shelter will not reveal proper scientific data. It could yield 100 artifacts but if the shelter is home to a burrowing critter or two, the shelter is essentially worthless for study.
Get a digging buddy and share with him/her. Digging solo is hard. Be able to recognize ALL artifacts. I have found hundreds of tools (especially scrapers) in sift piles simply because the previous diggers had a certain shape (arrowhead) in mind when they dug. Don't worry about graves, they are seldom found in rock shelters. Unless you're in the arid Southwest, you'll never know if you're digging a grave because mother nature will have already reclaimed the organic matter.
Pics would be awesome but all of us understand if you don't. I always post pics of my shelters because I don't worry about someone being able to find the ONE shelter that I'm digging in....lol...I mean....how would they find it?! It's not like there's a mile marker or similiar feature that gives it away.....best of luck.