Splitting causes signal loss. One question is whether your property can be served with a 3-way split as the cable's been already split for two neighbours. Ideally another cable should be pulled to the property when service becomes available.
cables can be split - not ideal i agree but the OP has not been told thats the reason - in fact he has not been given any reason - if another cable is needed then that would be done - it does not take 18 months for that to happen
It seems to me that a terrace house was converted into two leasehold flats. The OP referred to a neighbour next door which sounds like the house next to his. To take your example you could have the ground floor flat 54a Round St where the OP lives with 54b Round St upstairs and 53 Round St next door, with 54b Round St and 53 Round St having VM service from the cable coming into the OP's front wall.