Could be lots of variation Lon, depending on your local conditons.
The materials I buy have lost .001", remained the same or gained .001" after washing twice, both cold water washes - 1st with soap, seocnd is a wash cycle without soap - super rinse, I guess it is. That total .003" difference between the different weaves from ticking to different makes of denim. Seems to me, it was the ticking that gained a thou., probably due to shrinkage.
What temperture you wash it in might also matter as in, if you want it slightly thicker, use hot?
What I know about humitity in storage, is in my basement shop, the humidity remains pretty much a constant DRY condition, the cloths remain the same thickness, day in, day out- no matter when I measure them- pouring rain outside for 2 days- still dry in the shop. Come in with black fouling on a ML due to moisture in the air when shooting and in 20 minutes, it's white, inside the bore and outside. It's like a big de-humidifyer in there. It must change, but not much.
When shot for score, all my patches currently, are dripping wet with a WWWF/mix with some neetsfoot oil. Seems to work fine. I do take the calipers or mic to the store (when I remember them) - has worked for me, since the 70's. Every time I forget them, I come home with cloth that is too thin. It feels thick enough in the store, but will range from .014" to .018" normally - if it remained the same or take a thou off after cleaning and the new .018" is too thin for shooting well in my guns.