Double snowdrops

[Menai]

I hope you serious galanthophiles won't scorn a couple, probably simple, questions from one who has never moved on from the "pretty drift of snowdrops" attitude to the genus.
My sister has had a typical Oxfordshire village garden for nearly 50 years - about 100m x30m surrounded by high walls, with a few old apple trees and in spring, sheets of snowdrops in the corners. While I was working in it a couple of years ago I noticed she had a nice clump of doubles and then I looked closer and realised that all of her snowdrops were doubles and very uniform. I spent about an hour searching and found not one single.
My sister, who hadn't apparently even noticed she had doubles, says she has never planted any Galanthus. They were just there.
I know that the doubling gene is dominant and that doubles can produce viable pollen but wouldn't one have expected some reversion to the normal single over all those years?
Are these a named variety?
Sadly, she is having to move out and sell the house this year. Should I remove some of these plants to save what must be a very stable clone. If so how do I keep them unadulterated by my random singles?
Photos attached

Erle

[johnw]

Erie  -

It is always wise to perpetuate a good vigorous snowdrop be it common or not. It might be wise to take a very close look at them to see if there are any odd ones amongst them - odd is good.  Most likely they are perpetuated vegatatively from the original clump of doubles, either in the process of raking up or just rolling about round the yard.

Things get more complicated when they are singles in the mix.  It would be easy enough to find out the percentage of doubles in a single x double cross.  Sadly little work is being done in this regard save for that of MartinB who regularly posts on these matters.

johnw      - +3c and temp slipping.

[Alan_b]

Doubles may be able to produce viable pollen but they cannot set seed so in a population that consists exclusively of doubles you can be sure they all increased by division of the bulbs.  What you have are some good examples of the double form of galanthus nivalis.  They are quite uniform but there are some double snowdrops that are much more so; one called "Ailwyn" springs to mind http://www.srgc.org.uk/forum/index.php?topic=6216.0 .  

But I'll go along with what JohnW said; you like those snowdrops so save some and spread them around.