Ive found most leaks are around the tape and especially at the vacuum intake and outlet at the bag seal.

I'm the king of micro leaks and eventually you have to admit defeat and re bag it.

if you can get a second person to watch the gauge you may be able to find the leak by slowly working over the bag while they watch as the speed of gauge drop changes as you touch it.

to answer your question if you do not have a digital vacuumreader you can get "full" vacuum on the gauge with a leak.