Hi,
I think those two deaths are the same - when I looked it up I found Billington then as you say Blackburn on Free BMD. Genuki says Blackburn Register Office covers Billington.
I suppose it is that the age is the same for that Leonard Madden. As Emms says, the names strike you as all Irish descent and there could well be another Leonard turning up later- who knows?
Well there must be as there are two marriages

Although they could technically be the same person.
There is a birth 1905 in Ardwick and 1 living in Oldham who is 10 yrs old in 1911- he could be the one who marries in 1925 and even 1936.
Also Madden could be open to several spelling errors.
It's a pity they don't give a church for a funeral as they do for some marriages on Lancashire Free BMD

At the moment I am strongly in favour of the chap in Blackburn but ..why there?
good luck
heywood