I think there are different nuances in meanings on this aid of the pond, which is why, for me,William Posters alias Fred Johnson which would prompt an AKA is different from William Posters, goes by Bill. Some people will record a diminutive as part of the main name eclosing it in quotes.
As far as the composition of names is concerned with census records I record in the memo field of a Census event (I use Reunion therefore the description field with FTM) the name as enumerated if there is a material non-spelling difference. American Census records though I find can be unreliable in all respects far more so than British ones. I recently for instance had a male who was described as widowed and a few lines down the page was his dead wife in a different household after also having been widowed.