One way to discover whether your theory that pants are shrinking is to take a tape measure and measure them. close them up, and measure from the seam at the back of the wasit to the closure, then multiply that by two.
Haband is normally exactly the correct measurement: I have found much more variance in dept. store pants, which cost double the price of Haband, and then they charge you for hemming them up, which must be done unless you are 6'5" or so.
Haband can make mistakes (or their Chinese pantsmakers, who stick the size label on), but they will always take them back.
When I buy a pair of pants, if the size is not on a permanent label, I write it on the back of the waist with a magic marker.