You could contact Treorchy Library and ask them for a copy of the interment record, along with interment records for anybody else buried in the plot - this will give you the details of where the people lived who reported the death, the date of the funeral etc.
If you go to rctbc.gov.uk website,(rhondda cynon taf) look for leisure libraries culture click on libraries and then locations and opening hours, click on Treorchy and it will give you a link to their website - sent them an email requesting the info and they will come back to you when they have it