Target hygrometer reading in a sealed mason jar after the reading has stabilised, so after more than 24hrs, is between 58 and 63%.
I aim for the higher number always. Worst I've done is mid 50's, doesn't smoke as well as low 60's, loses terps and the cut grass hay smell is starting to creep in. No don't lost potency also.
I have stored them in jars for many many years and it's not unusual over that time to lise a couple of percentage points on the moisture. Weights typically don't vary much either if properly dried and cured.