Hi Frank, no problem.
It's written here:
http://www.trenitalia.com/tcom/Treni-Regionali/Viaggiare-in-regione/Il-biglietto-e-l%E2%80%99abbonamento-regionale-online
If you don't speak Italian, you could google translate only this paragraph:
Novità
Da oggi puoi acquistare il tuo biglietto regionale per viaggiare quando vuoi (decade il limite dell'acquisto da 7 giorni prima della partenza) fino a 20 minuti prima di partire.
As I did in a previous post, I've taken a print screen of trenitalia's "buy" pages and circled in green the date (6-.10-2016) and the train category (Regionale # ).
http://s23.postimg.org/g98vrgdqj/Rsteves.jpg
I don't know why you couldn't obtain the same result last night, but I hope you'll trust me anyway even if didn't actually buy the ticket.
The print screen shows that you can now buy regional train tickets more than 7 days in advance, I've entered June 10 as departure date because of the limit of the next timetable change of June 11.
The 120-day window gets smaller and smaller as you get closer to the date of the timetable change, and then, the day after, it widens up again to 120 days. This happens only for Regionale trains that are subsidized by regional governments and are always the last ones to be loaded in the system. No competition from Italo... no "real" money from passengers ... no hurry. Trenitalia hates us all.
You are absolutely right: Regional train tickets bought in Italy (at the counter, at authorized travel agencies or at Tobacconists) come with less restrictions, but many tourists seem to appreciate the fact you don't need to validate tickets purchased on-line.