....so you mixed your salt and water, sealed them up, they got to 65% and you think they are calibrated..??
Ohh Kay.....
First off, you need to focus on the test environment. If you're stuck with ziploc bags, I found you pretty much have to double bag the environment. If you can't run the test twice in a row and get the same results, you have a problem. I found that a mason jar, or even an old mayo jar works FAR better than bags.
Or, spend eight bucks on one of these and you'll know for sure:
https://www.amazon.com/Boveda-One-Step-Hygrometer-Calibration-Kit/dp/B000A3UBLA
Sorry if I'm coming off a bit cynical, but if you're going to take the time to calibrate your hygros (and you should).....at least take the right steps to see your efforts pan out. Just because you're in a hurry, doesn't mean the cal is valid. "Triple redundancy" can mean you have three incorrect RH readings, so calibrating them is pretty important. Most small digital hygros are not accurate, out of the box. Most analog versions are even worse to the point of being virtually worthless.
Oh, and you did start with fresh batteries all around, yes...??