They used to have a marker that identified BT based lines.
Note this is NOT BTretail but BT Wholesale line rental (WLR) which in brief is basically any ISP not using Full Metallic Path LLU.
I used that marker as an aid to note which map to prepare for line length and the visual map markers.. knowing that no data would be returned for LLU lines therefore no point doing some of the steps. There's actually 4 different map formats which depend upon data input by the user and data returned from BTw.
So the marker has gone, but BTw is still returning line data which likely means they stopped the marker for some equivalence rule or other (guessing!)
As it's not actually affecting the end results other than saying 'possible not BT line' it really is not a priority right now. I'm up to my eyes in other admin work and keeping the site running. It's no fun these days trying to run a site and keeping everything compliant and up to date.. because the amount of background stuff that no-one gets to see is no mean feat