Hi Jen
When people filled in their census returns 100 or more years ago, they had no idea that we were going to be using them for research. In fact they were probably told that the contents would never be made public!
In many cases they could have been illiterate, or semi-literate, and like a lot of people nowadays, not bothered about whether the information they gave was accurate or not. They would put down whatever the person was known as, regardless of what they had been registered at birth or baptised - and these aren't always the same.
In addition, a lot of returns would have been filled in by men and (sexist as this is) how many RootsChatters know men who would be pushed to tell you whether their wives
have a middle name, never mind what it is

My Dad had 1 sister, 1 wife and 2 daughters and in the heat of the moment would often run through all our names before hitting on the right one (and his sister lived 50 miles away).
I tend to use
all the information given on each certificate or census and weigh up the probability of it being the same person. Of course you risk following up a wrong lead occasionally, but very few of us can be absolutely sure that all the research we have done is 100% accurate.
There has recently been another thread on how much 'proof' you need (or can expect).
Go with what you find, and when searching for new stuff use all the variations you are aware of. Oh and don't make assumptions. I had always assumed that Frank was short for Francis, but there are many Franks in BMD and census records.
And finally - I once knew someone who was always known as Biddy. Her given name was Jessie

Linda