(10 Jun 2016, 7:27 am)Sinky wrote Does the 19 still interwork with the 1/5/5A/12?

Yes, but the 12 and 19 don't interwork with each other, this is how the interworking patterns work on the 1, 5, 5A,12 & 19:

1 Darlington - Bishop Auckland.
5/5A Bishop Auckland - Darlington.
12 Darlington Town Centre - Hurworth.
12 Hurworth - Middleton St George.
12 Middleton St George - Hurworth.
12 Hurworth - Darlington Town Centre.
1 Darlington - Bishop Auckland.
Journeys that arrive in Darlington Town Centre as service 5A go onto service 12 whilst journeys that arrive in Darlington as service 5 lay over for 15 minutes then do the 1 to Bishop Auckland instead of going onto service 12.

5/5A Darlington - Bishop Auckland.
1 Bishop Auckland - Darlington.
19 Darlington - West Park - Darlington.
5/5A Darlington - Bishop Auckland.
The 5/5A don't interwork, the interworking pattern is: 1/5/19 and 1/5A/19.

So basically, if you see something odd on a Darlington bound 5/5A, it interworks with the 12, if you see something odd on a Bishop Auckland bound 5/5A, it interworks with the 19.