Quote: "I know on video the British DVDs have been derived from the 29."

Yes, but British video is always rather erratic. Remember, when the complete British version of "Mother Riley Meets the Vampire" was shown on several British TV channels (I got a VHS recorded from Channel Four), the only source then available on video in GB (on VHS) wasn't the British version, but the cut US version, "My Son, the Vampire"! (this was years before the release of the original version co-billed with another Old Mother Riley movie - and four others if I remember well, in recent years).

So, they could have released the 1929 version on DVD even if the 1925 original lies in some archive...

I wasn't specifically thinking to UK or France. As we can imagine, POTO was probably released in a lot of countries. Some of them probably never had the subsequent version. So, a print of the 1925 original COULD be in some European or Russian archive - who knows?