It's possible if you add them like that (i.e. with both values at once for a single key entry of 'Jan'). So long as they value type is 'any' (which I think is the default) then you can store them like that, but you have to do the work yourself manually to add new elements, which is something I do in some cases.
i.e. search if the key exists, if not then add it as normal, if it does get the value, concatenate with the new value and re-set it.
