On a related note, somewhere in Dickens there's a character who invented the name "Morleena" for the special distinction of his daughter ... presumably a blend of
Maureen and one of the -ena names. Clearly not a forerunner of
Marlene, but a sign of what can happen when parents do name mergers.
The 18th century seems to have been an interesting period for naming babies, at least in Britain, with
German names echoing the royal family, former nicknames like
Polly being used as given names, and - I think this was in an old edition of the Oxford Dictionary of
Christian Names - the truly horrible Frusannah, a mixture of
Frances and
Susannah. Presumably it must have been used more than once to show up on the statistics ... and perhaps it was part of a trend that also includes your
German merger names?