Hello,
I hope that you do not mind me butting in - I discovered your post while doing a general search. I am a maker, researcher and teacher of passementerie (textile trimmings - in particular historic items) and so was very very excited to see this beautiful sampler.
Whilst I am not an expert in the lives of button makers in Dorset or elsewhere, I do know a bit about their general history and can perhaps give you some extra info, if you are still looking. The industry itself was actually quite massive, and while makers worked from home, many people earned their livelihoods making buttons - as I understand it, when the industry collapsed thanks to the button machines, many families left for Australia.
What is particularly interesting in your sampler, from my point of view, is that at least four of the buttons are types that are usually found as decorative coverings for satin-wrapped or cloth covered buttons not normally, as far as I know, associated with the area. Don't get me wrong - there are some that are associated, as have already been mentioned - the Dorset Knob (which appears to be the first one, second row), High Top and various 'Singletons' (singletons were still made using rings though, not on the padded shape shown here)- And so, the sampler perhaps sheds a little extra light on what was taught, as in 1914 there really wasn't an industry left at all (there was a slight revival attempted by Lady Lees but only generated £38 in 1912 - with expenses of £36!)
I would love to be able to discuss your sampler in more detail with you as I think that I may be able to tell you how most were made (Though I cannot see the details of the stitches in the image posted)
This recent publication might be of interest - "Dorset Buttons Hand Stitched in Dorset for over 300 years" by Thelma Johns