It used to be possible to purchase regional train tickets for a given milage (e.g. 100km) from newspaper stands / tobacco vendors at the station. You would purchase such a ticket for e.g. Florence->Pisa and could use it within some 3 months I believe, by stamping it before the start of your journey. Of course you were also free to travel in the opposite direction with the same ticket.
Trenitalia has recently changed their rules for regional train tickets (in an effort to stop fare evasion) so that any paper-based ticket (no matter whether it was purchased at the machines, ticket counter or from a newspaper stand as mentioned above) is only valid for a certain date, until 23:59 on that day. (Online tickets and tickets purchased via the app are mentioned as an exception but in reality those already are implicitly stamped as they can only be used during a restricted period of time.)
My question is, can I still use a train ticket for the opposite direction of travel, e.g. Pisa->Florence when the ticket is for Florence->Pisa? With the old kilometer-style tickets that was not a problem (I could also have used those for a different journey of the same or shorter length) but how about the new date-fixed regional tickets? In my example the ticket would be stamped (convalidated) in Pisa and I'd be on a train from there to Florence, the cost of travelling either way being the same.