The fabric does "fluff" after washing and drying so a light pressure measurement will change, But the "crushed" measurement stays the same.
"Crushed" is when the fabric is pressed tightly in caliper or micrometer jaws, it's that measurement that more closely mimics what happens when fabric is used as patch between a lead ball and the bore of the rifle.
Guy's will argue that a caliper measures differently then a micrometer,, and they're right, it's about the amount of fabric that's in wide jaws vs a small round micrometer.
But it doesn't matter because your measurement only applies to you. You are comparing fabric for your use. Whether the measurement is .010-.011-.016 or .020 with the tool your using,, it only affects your use of the fabric.
Your use of your tool is the only thing that matters, as long as you use it the same way all the time.
Get it?
So yeah, fluffy soft measurement changes after washing, crushed doesn't.