BlueMorel wrote:
Occasionally while digging through boxes at home I find packets, some unopened, of various photo printer papers or card stock type papers from the last 20 years, including some t-shirt transfer paper from the late 1990's. Will it damage my 2019 Canon Pixma Pro100 printer if I try it out?
I don't think that you will damage your printer by using "old" paper in it. My experience has been that some (but not all) old photo paper becomes stiff and/or curved and won't feed properly through my Canon printer. Then I just get rid of it. New paper isn't terribly expensive.