Digging deeper into your enquiry I learnt that Dorothy, Ann & James deaths were all registered in the Plympton St Mary registration district. Yealmpton is included in this district.

A search in the Online Genealogical Index (OGI) shows that there are no burials anywhere online for Yealmpton post 1883 & the Devon Heritage Centre (Records Office) also does not have the register of burials at Yealmpton post 1883.

Therefore the conclusion is that is must still be in the hands of the incumbant or less likely lost.

My next move would be to contact the the parish again.