This is bewildering. I am in South West Wales.
(in what was Demetae territory, but I am close to the border of "Siluria")
No one here has been celebrating nos Galangaeaf.
They are all geared up for Bonfire Night though, on Nov 5th.
And it seems all those "winter's eve/end of summer" festivities will be on Bonfire Night.
I am having a huge discussion with people over whether it is "galangaeaf" or calan gaeaf". In my welsh dictionary it says "nos Galangaeaf" translates to "Halloween".
See although my grandad used to speak Welsh, he was discouraged from doing so as a child, in England. So we weren't brought up as Welsh speakers.
Also, now that there is a revival of Welsh language in Wales, they have standardised Welsh. It is all a bit confusing. There isn't truly a standardised Welsh language; there a sometimes huge regional differences.

Still wondering what's correct. I even have a new academic book that incorrectly says nos Calan gaeaf is celebrated in February. :O I had that woman as a professor of folklore a few years back! oh dear!