Hi Roy,
I based my thoughts on the house address, in that Gelligaer came before Pontlottyn on the address. Pontlottyn has a Station Row, but not a Railway Terrace. Although, there could have been a Railway Terrace in the past.
I live in Pontlottyn, and now our address is Pontlottyn, Bargoed , Caerphilly. This is confusing for anyone, especially when we get a delivery.
I think your suggestion to check with CCBC is a good place to start. Assuming the records were archived responsibly over the changes.
Rhymney Valley District Council took over from the older authorities of Gelligaer Urban District Council, and then in 1996, Rhymney Valley District Council was amalgamated with Islwyn Borough Council to form Caerphilly County Borough.