CAN you fix anything now for advance-then simply check on the sites how much tickets cost. Then you do not have to worry anymore about pesky REServazione etc-but also not change plans anymore. connect-sncf for FR and renfe.com for ESpana. Or allin: sites like trainline-these charge a little extra fee, but many people find booking via them easier.

With an IR there will ALSO be quite high supplmts to pay-depending on what train you take, but you use exactly the 3 counties that are always mentioned as being very nasty to passholders, in particular ESpana. Other general sites always advise to book fixed before to avoid all that trouble.

But in FR you can take local=TER treni without any surcharge on a pass=takes longer, more changes. Ditto for MIlano-Frontere FR (Ventimiglia). In ESpana not. And its very. very often said to be hell for passholders in main summertime (and also crazy hot in inland)