Yes, always mark duplicates!! I've had to give 2 to a couple over the years but I don't charge for them. It can sometimes be annoying but it's less than 5 minutes out of my day so I've never worried about it. Having to write 5 would definitely be annoying though! How unorganized can one person be?? Lol

This is also why I don't write my SIN on them even though many will tell you that it's required. I don't want my name and sin floating around god knows where!!