Whilst what you suggest is always possible, the changing of proper nouns in songs and the changing of dates is very common, both deliberately and due to forgetfulness, to modernise/relocate a text. The texts listed above vary considerably and are only recognisable as being related in some cases because they use the same key lines and phrases or even whole stanzas. The merging of several earlier songs into one new song is also quite common. Cecilia Costello's 'Grey Cock' contains elements of 3 identifiably separate ballads, which doesn't mean that she took these 3 ballads and stuck them together, it means somewhere along the line of evolution this has occurred for whatever reason.

Regarding dates, I can quote ballads that have numerous versions and in every single version the date is different. This one must at least be down mainly to oral tradition if not all oral tradition.

There is also the possibility in there that Phil took stock phrases himself from existing ballads, although I haven't come across these yet.