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In other words, Zürich, Fernsehstudio is located on the border of Zones 121 and 110. So if getting a return ticket from Herti (also zone 121), the system will only sell you a 1-2 zones ticket for zones 121 and 122. Even if you actually don’t need zone 122, as a single zone ticket such as 121 only does not exist in the ZVV (only “Kurzstrecke” short distance single tickets). Therefore your 121, 122 ticket was not valid when you got caught in zone 110 (Zurich City).
The reason why zone 110 (Zurich) was not included instead of the “useless” 122 with your itinerary is because 110 counts as two zones due to its size. You’d notice that you get a 3 zones ticket from Herti to Zurich city, although the journey includes only zones 121 and 110.