I read about a couple being fined recently for getting off their train at an earlier stop, so I was worried I might be fined for getting on at a later stop on my journey back because of the terms and conditions of the off peak return.
I very much doubt anyone has been
fined for this. People have been charged an additional fare for finishing short, in one case a couple paid up but moaned about it, however they were on a Megatrain ticket, where it is made very clear that it is banned, so that case isn't particularly relevant to National Rail ticketing. They were also on a penalty fare train, although that may or may not be relevant. The only other case I'm aware of involved the Prof from Durham, when EC staff allegedly didn't adhere to policy of letting him through and charged him a ticket (although some EC staff dispute that, saying that their staff would do this) anyway, whatever happened, he didn't pay up front, and was issued with an Unpaid Fare Notice, which East Coast cancelled immediately, and apologised for this.
Starting short when banned is different, and you could be refused entry if you refuse to buy an additional ticket, at the barrier (some people say that a ticket from the station you join at to the origin means you have paid the correct fare, and you can then simply not bother double-backing, however that is a debatable point).
It's a can of worms that has been done to death on this forum (try a
search).
As you are on the
return portion of an
Off Peak ticket, you should have no problems at all.
The incidents that you have heard about were, almost certainly, on
Advance / Megatrain tickets.
Oracle, am I right in thinking there used to be a direct train from the Bournemouth/Poole area to Aberdeen? If so, when was this service discontinued?
I am sure there would have been! There have been many changes over the years, with less and less direct trains and more emphasis on 'clockface' timetables where trains go to the same places each hour (or half hour etc) and you have to change.