Neath is in Glamorgan and not Breconshire?
For registration purposes a great deal - if not the whole - of Glamorgan came under Breconshire, 100 years ago, at least.

Neath itself was part of the Neath Registration District.
Neath RD was in existence from 1837 to 1970, and consisted of 30 parishes in Glamorgan, and 3 parishes from Breconshire.
Merthyr Tydfil RD contained 2 (out of 9) parishes that were in Breconshire.
Pontardawe RD contained 2 (out of 7) parishes that were in Breconshire.
There are no other Breconshire parishes in the remaining 7 Registration Districts in Glamorganshire.