Nope. An FTTC cab is only ever connected to a single PCP.
If the FTTC cab you've found is next to a BT PCP with a different number, then the chances are that it has nothing to do with your line or cab.
Where I am sitting right now, there are 3 PCPs within 40m, each with 1 FTTC cab. They aren't always a long way apart.
In almost every deployment, the original PCP (steel, cast iron or fibreglass) stays in place. The (vented) FTTC cab is always a nearby addition.
Was Zarjaz's earlier post not a link to your particular cabinet? With the FTTC cabinet down a side street? Or was he just giving an example of a hidden FTTC cabinet?
No, not at all, as Zarjaz points out he gave an example of where an FTTC cab may be hidden around a corner.
All I can do is see if there is an FTTC cabinet hidden in the vicinity serving my PCP directly. I'm surprised that although the nearest visible FTTC cab resides 40 metres down the road with it's own close by PCP, is it not practice for cabling to link two PCP's together?
If so (and within a certain distance ie say less than 50 metres), the FTTC cabinet (down the street) could be indirectly connected to by my PCP by going via it's PCP first? That could be done in theory but is it done in practice?