"Acually, there were a number of early sonnets ( Wyatt and Surrey) that were 18 lines"
,..,
My recollection, Bruce, is that the inclusion of these within the "Sonnet" definition & category has been a subject of some taxonomic debate & disagreement within the prosodically defining part of the academic community. I probably read all about it at some stage during my undergraduate days, 1952-55. But I honestly haven't the energy to go back into it again ~~ a bit like Mr Brooke in Middlemarch who, you will recall, constantly claims to have "gone into all that at one time". So I will concede that you might well have a point here; but OTOH...

Best regards anyhow
~M~