I just bought a 7 day season ticket this morning when I noticed the letter "A" at the end of the expiry date. The last time I bought the same ticket on the same route, there was no letter.
Does this signify anything important (such as the ticket expires in the morning on the 20th)?
According to the wiki...
Advance dating indicator: If an A is present next to the date, the ticket was bought before the date of travel. Standard travel tickets can be bought up to one year in advance.
Source: APTIS Ticket Features
After changing trains I asked the guard on the subsequent train. It turns it means that the season ticket was bought in advance of the start period ... and now I see that it was, of course 20th March is more than 7 days away: the guard on the last train has sold me the wrong ticket. (I don't know why he would sell me an advance ticket when I was already on the train.)