I had an office within a block that was supplied UG from 3 local cabinets.
The address checker suggested from a cabinet which was a very slow ADSL service, but a tweek of the address found others might be on FTTC.
Eventually we ordered FTTC broadband using the 'generic' site address and on fitting day I met the Openreach engineer and explained what we'd found. After a little bit of head scratching and realisation that there were spare pairs for the right PCP he run a new cable from the internal wiring to our office and happy days it worked.
But, my understanding is a lot will depend on how the local network has been built, where there is spare pairs and do the pairs from the PCPs nearby actually cross over each other. As an example my home has one PCP for the whole estate- you've no choice it's from cab121 or nothing! Luckily we're FTTP here so don't have that problem really.