The index is designed as a pointer to information on individual Parish Clerks (and other roles) which is not easily accessible by other means.
So, for example all references from Ditchfields book and other printed resources that I have found are included, but a list generated by a blanket extraction from the 1881 census index is not.
The index only contains references to parish clerks from before about 1907. After that date, the role changed substantially and that of the modern parish clerk is very different – they are the clerk to the parish council and are part of the local government organisation. To maintain consistency, records for other roles such as churchwardens have a cut-off point of the same period.
Additions are always welcome and if the information you supply concerns an ancestor, please let me know and I will attempt to put you in touch if someone else contacts me about them.