Recruiters and recruitment agencies used to advise keeping your CV up to date so that you'd be all ready if a job came up, was advertised etc. I think the advice was to add to it on a regular basis, adding any new skills, new roles and so on. I 'wouldn't put a job on my CV' if it was only to say 'I have been at ABC Dentists' for the last two weeks', that seems a little pointless.