It appears that, just as Fastershire said, BT Openreach is doing work to enable at least some fibre in the “Exchange Only” affected area. The solution appears to be to cut the lines directly into the Exchange and run them through a new cabinet on Greenway just outside the exchange.
I have reason to believe that there is a list which says which numbers will be enabled. I do not know if this list includes all of the exchange only numbers or only some. And I do not know who produced the list either for or at BT Openreach, or what criteria were used to produce it.