I can't tell you who to believe, but their reply says it will not show up on a paper boarding pass, and I have several paper boarding passes (both agent and kiosk printed) where it does show up.
As always, YMMV
I as well. As noted (and shown above) it will have "ID" appended to the TSA PRE CHECK" verbage on a paper boarding pass. (Mobile will also have the special logo. Can't say about kiosk printed poasses as I don't use them.) NOW, all of these times
I initially checked on on a mobile app, and just got a reprint when checikng bags, etc from the agent. Perhaps that is key - where initial check-in occurs??