Hey highres...take us a low res so we can see what you are dealing with.
I've pretty much seen the gamut of drywall destroyed by shitty workmanship, bad materials, age and mold...but I can't tell without a pic.
Twenty years puts you in the era of really bad construction techniques in Vancouver...they were knocking houses up so fast that no one cared, so I'm inclined to believe in just crappy workmanship.