Which public transportation ticket should I buy in this case?

Transportation, Travel and Trips
1
I have the "9 O'clock Zurich" ticket (see here ) which includes these zones:

Now I want to go to Regensberg in zone 112. For this I have to buy a new ticket, which I could buy from Zurich HB but in that case I would be paying 4 zones (110*2 + 121 + 112). I can buy from Oberglatt and in this case I pay only for two zones (121 + 112). Now, zone 121 I already have so I am wondering if there is a way of paying only zone 112 which is actually the one I am missing. For this I would select in the SBB app a 24 H ticket from Dielsdorf to Regensberg, which should give me only zone 112. Would this be correct?

2
I think you are correct

3
No, because your current ticket does not take you to Dielsdorf.

You have to pay from the last station your train/bus calls within your allowed zones.

It's quicker if you buy an extension ticket (Anschlussbillet) which unfortunately has a minimum of 2 zones.

So the Oberglatt solution you mention would be the right one.