I might mention my cousin's work on the family tree.
Though this like the mobility of workers might be conveniently overlooked
She began working on the tree well before PC's started to be commonplace domestic appliances
Thus much of the data she obtained was 'offline'
I have understood her to be meticulous
Even acknowledging situations where lineage is to be queried
Thus I have seen no cause to question accuracy of her charts
My parents also did much family research before the advent of PCs (and they never did use a PC). Apart from very local information, they did most of their research via the LDS Family centres. The IGI existed long before it was available online. The LDS family centres had much information available for those of us living long distances from the original parishes or country records offices.
Have you actually ASKED your cousin if she accessed the original parish records? Does her research document sources (much as I loved & respected my parents I have found many errors in their research when official registers were checked). It is, of course, entirely your own affair how much research you wish to do, but my suggestion would be to check original parish records and/or the official birth records for those children born after civil registration.
Good luck with it
Trish