I'm always wary of diminuitives. They often turn out to be very much of their time and place. And misinterpreted by the clergy.

My C18th Lucy has descendants called Louisa. I suspect they were all called Lou, but given a different gloss in the C19th.

My Millys in Surrey clearly did not pay any attention to what the officials thought, as they appear in official records as Amelia, Emily or Millicent. Millicents will turn up as Amelia, Amelias as Emily.

I think a lot of clergy assumed names were diminutive when they weren't, and the peasantry was too polite to correct them.

I've told this before, but in 18th and 19th century Darwen, Lancs, the name Mally was very popular. The vicar of the day refused to baptise this godless name, so they were baptised as .Mary and never used the name Mary again.

OC

Maternal great aunt was Mary Ann Elizabeth,known as Doll - never did find out why.

Her sister was Jane, always referred to as Gin, which is a bit more understandable.