Hmmm, a little piece of my tiny mind has just remembered a few months back, when on an FTTC repair job and the modem/router would attain synch, but would not get a PPP session going.
All the network/port/mapping etc was correct, so I was asked by our DCoE to ring the ISP to see it their 'build' matched Openreach's 'build' on their records ??
I was then given a C-tag number, an S-tag number ....... and also a BBEU number ............. so you are right in your assumptions.
I've never personally heard of a NGA10 Network Eelement, sorry.