I hope this isn't too late and this hasn't already been sorted out, but
just in case here goes.
Lancelot du Lac = Lug Lamhcalad
OK, well first of all I can't see how the name Lug becomes of the lake,
different spot in the name, one at the end one at the beginning, if Lug
were the name they were trying to modernise then it would appear in the
name not in the epithet.
Secondly Lug was the sun-god of the Celts, nothing to do with lakes or
oceans, his name appears from Iron age 'magical' inscriptions from Gaul
as Lugus, then in Irish as Lugh and in Welsh as Lleu.
With the lamh = lan thing, well unfortunately the letters 'mh' in Irish
correspond to the English letter 'v' as far as sound is concerned, so the
apparent similarity with 'Lan' is not in fact real, they come from
completely different sources.
Celot = calad. Of the five sounds represented by Calad four of them do
not appear in 'celot'. The hard 'c' of calad is not found in Lancelot,
making those sounds not corresond. Calad had originally come from the
word 'caleti', so the 'a' has always been an 'a' and not an 'e'. The 'l'
is admittedly the same in both words. The 'e' of caleti had changed
through affection to an 'a' - perfectly normal - but it was never an 'o'
as it would have to be for it to bear any resemblance to 'celot'. The 't'
of caleti has been lenited, or softened to a 'd' in calad, it does not
then harden again to be a 't' as it would have to.
I hope this all makes sense. Lan does not equal lamh
celot does not equal calad
Lac does not equal Lug.
Lancelot is not therefore a later version of this figure, and he does not
belong in any repetoire of Celtic figures, he was an invention of the
12th century frenchman Chretien de Troyes.
Mark Handley, Trinity Hall, Cambridge.