From your first post. It's just the reverse of what you have. UN&PWD for FTTP, UN,PWD,VLAN for FTTC.
Always been the case
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In the early days of FTTC when routers didn't have VDSL modem chips, Openreach provided modems for you, these did the VLAN element so you only needed UN&PWD. Some people keep one of these modems in a draw just in case (yes I have 2).
When the routers progressed ot having VDSL modems that's when needing to VLAN tag on the routers started to become a thing, it was similar earlier with ADSL needing VPI/VCI as well.