Possible sport Campanula Lactiflora.

Anybody know lots about the above. I have grown Pritchards Variety for years as below.

It self seeds a bit and usually comes true ie blue. It sometimes produces paler blue and a near white a la below.

However, this year after having grown the plant for over 25 years I noticed this...

It is pure white, not milky in any way. It is being swamped by a Cephalaria Gigantae currently.
Anybody know if it might come true from seed or when to take cuttings, root or softwood? Once bigger it will be a really nice addition to the borders and there are not that many pure white herbaceous perennials that flower at this time of year. I doubt I can lay claim to a new plant as such but it certainly is the first time I have got a white seedling.