I agree that BT seem to getting themselves in a mess over it.
The snag is that it is not like building a car for example where the processes are known, the variables controllable, and the outcome can be determined.
Here is a (only slightly) invented example of what can go wrong....
Ducts to cabinet from exchange blocked.
Original ducts put in Post WWII early 1940's ran over land which now appears to be private hands, and there is now an ornamental hedge on top of them - which is probbaly why they are blocked - the roots have got into the ducts.
All BT/GPO paperwork for original installation lost - no records in land registry of BT plant on the land, all land deeds also lost as to whom owned what when.
Hedge clearly obstructs the right of access to BT to maintain the duct - which hasn't been touched since 1940.
So BT either need to unblock the ducts (dig up the hedge) or arrange for a totally new route.
So BT approach land owner - he denies everything saying hedge put in decades ago and its all nowt to do with him as he did not own the house then.
BT now need to get lawyers involved to seek a solution.
Either they need to dig up the hedge, or they need to create a new wayleave (right to run and maintain plus rights of access for a utility service) over the private land and run the cable/fibre round the obstruction - which also means new joint pits at either end to re-connect to existing ductwork.
Well this is good for easily 6 months+ of argy bargy as both sides argue about how,why,what,when,how much and generally about everything and anything.
Then when you think you are sorted...... a wretched gas pipeline where you want top put the Fibre box which you discover when you start the installation. The gas board's map shows it to be on the other side of the road - but obviously the persons who actually did the job 30 years ago thought it easier to use the other route and no one ever updated/modified the gas network records because ...well they couldn't be arrrrsed. So either the fibre box has to be re-located or the gas main moved.
and so it goes on and on............................
I would agree with you that being given a date SHOULD mean that the cabinet has been marked for upgrade and is not one that is deemed economically unviable or is not to be upgraded under current plans for a variety of other reasons.
The reason I hesitate is that there have been some instances where a planned upgrade has been abandoned. This usually has been because someone in the middle is being totally obstructive and BT not suprisingly have said "sod it - let's move on somewhere else where there is less hassle".
One known example was a council objecting to the siting of a cabinet located in a conservation area - only in such areas are BT required to seek planning permission. In other areas they use their statutory powers as a utility company to basically do what they like. So BT scrapped the cabinet roll out and moved on elsewhere.
To be honest I don't see why BT don't scrap all these estimated dates and say nothing at all.
It's a bit like when you are doing a job, it's starting to go wrong and someone keeps on coming up to you wanting to know when it will be finished.
You are up to your neck in trouble, you have no idea, but they insist on a time so you guess at tomorrow morning just to make them shut up and go away.
Come the next morning you ain't finished and everyone moans that you didn't meet the time of finish....forgetting that actually you gave the time under pressure to supply some info and it was a wild guess anyway 'cos you were up to your neck in sewage (or whatever) at the time.
