Not sure if discount still applies or about current rules of train stopping at last station in Zone.
When using a combination of tickets, if one of the tickets is a season then the train doesn't have to stop at the boundary station.
Or, as National Rail put it:
19. Using a combination of tickets
You may use two or more tickets for one journey as long as together they cover
the entire journey and one of the following applies:
(a) they are both Zonal Tickets (unless special conditions prohibit their use);
(b) the train you are in calls at the station where you change from one ticket to
another; or
(c) one of the tickets is a Season Ticket (which for this purpose does not include Season
Tickets or travel passes issued on behalf of a passenger transport executive or
local authority) or a leisure travel pass, and the other ticket(s) is/are not.
You must comply with any restriction shown on the tickets relating to travel in the
trains of a particular Train Company or Train Companies (see Condition 10).
If you do not comply with this Condition, you will be treated as having joined the
train without a ticket and the relevant parts of Condition 2 or 4 will apply, either
to the entire journey, or from the last station where the train stopped at which at
least one of the tickets was valid.
For the purposes of this Condition, a ^leisure travel pass^ means any multi-journey
ticket (excluding Season Tickets) valid for:
(i) at least 7 consecutive days; or
(ii) at least 3 days in a period of at least 7 consecutive days
and includes rover tickets, travel passes, flexipass tickets and BritRail passes.