Hello If you contact the local register office, and specify all the known facts, they should be able to find the correct certificate. Include parent's names, father's occupation, Parish/locality, etc should help narrow down the options.You are correct that Aberdare was included in Merthyr registration district:http://www.ukbmd.org.uk/genuki/reg/districts/merthyr%20tydfil.htmlBest WishesMorgan
I telephoned the Merthyr office and I told them them details of the couple's names and I was told that they did have a record for such a pair getting married. I asked if they would tell me the address and employment of Thomas Williams and I was told that they couldn't tell me anything and that to find out I would have to purchase the certificate. Is this unusual?