I have quite a few tickets for the underground/bus system in Paris from my last trip. Since then the price has gone up. Does anyone know if I can still use them or if I have to exchange them first at a ticket booth (and pay the price difference?)
The tickets are good forever. I have used tickets that were 5 years old. If by chance they have become demagnetized you can exchange them for fresh ones at the metro info or sales window.
From ratp site:
"You want to have an unused t+ ticket or old (mauve or green coloured) t ticket refunded
T+ tickets (as well as the old mauve or green t tickets) cannot be returned. They remain valid for use, with no time limit. This means that you do not need to exchange your old mauve or green t tickets. However, if they do not seem to be working take them to a ticket office or information counter where they can be checked. If necessary you will be provided immediately with a free replacement."
Your tickets won't be the old colored ones, they weren't selling those long before 2012. But yes, the ones you have are still valid if they've not been demagnetized in the meantime. It doesn't matter now what you spent for them when you bought them.