Celtic substrate influence

[Frank Rossi]

Recently, in another thread, I asked the following question, but no one
answered and, as I am still curious, I would like to put the question again
more specifically:

Given that:
1)  in North-West Spain, Galicia and Asturias, which are considered,
rightly or wrongly, the most Celtic areas of Spain, the two forms of the
past tense have been reduced in normal usage to one (the simple past)
and
2) a similar phenomenon can be observed in Northern France, Northern Italy
and SOUTH GERMANY, where in the Pre-Roman period the La Tene Iron Age
culture and presumably dialects of the Gallic language were prevalent if
not univarsal, although in this case it is the compound past that has
replaced the simple past,

Question:
Could there be a parallel influence of the Celtic substrate in both areas,
in the sense of a rejection of two forms for the past tense, i.e. either
the simple or the compound past, but not both?
What do the experts on Celtic languages think? In other words, are there
any similar phenomena in the Celtic languages, ancient and modern?

Regards

Frank Rossi
Bergamo, Italy
iglesias at axia.it