Yes - I had assumed that Jan was probably one of those names which was (or started as ) a variant of John. I think Kim is an 'as is' name in the UK when it is a male name, and **usually** short for Kimberly as a female one, although it wound not particularly surprise me to see it used as a stand alone for either gender.
I would assume that Kerry was female.
I remember a few years ago one of the Judges in our local court sending a plaintive letter round to local lawyers asking them to specific the gender of children's names when sending in a divorce petition. You see, on the paper work we had to complete at the time (it has changed, since) it just gave the names and dates of birth of any children of the family, but in the paperwork which the court has to send out at the next stage of the process, they had to specify the gender of the children, and the Judges were finding that they couldn't always tell, from the name, which gender a child was.
(I have recently come across a female Tyler, for instance)
We have to be quite careful to check whether the common short form of a name is the child's actual name, or whether they are really called the 'full' name but known by the shortened version, too