Linear B Greek has the Kw sound intact, in Ancient Greek it's become P. The timeline for Celtic is roughly the same, because it had not occured before the language was established in the Iberian Penninsula and Ireland, putting it in the Hallstatt era. PIE had broken up by ~2000BC at the very latest (and most think at least 1000 years earlier) so we'd be looking (in the absence of evidence from Linear B or Hittite) at the loss of a separate k'w in the early 2nd millennium BC. Therefore, Lusitanian would have to cling on to the separate sounds and/or undergo full labialisation 500-1000 years out of sync with its neighbours.

Also for the Epona-ists, there's the problem of Loiminna. If this is an epithet of Iccona, how can it occur on its own in Arroyo de la Luz? Normally double theonyms only appear when a Roman deity is equated with a native one (e.g. Minerva Sulis) but Iccona isn't a Roman import. I'm beginning to think Iccona isn't a goddess at all.