It's quite impossible to buy apples and produce scrumpy. Only 'scrumped' apples can make scrumpy.
Scrumpy is definitely not a type of cider - nothing whatever to do with low tech production or cloudiness. The term relates to the origin of the apples from which the cider is made. It should be noted that smaller scale cider makers are more likely to produce scrumpy than the bigger producers who have records to keep!
Apples of any variety come under general rights of ownership. As every inch of the land is owned by someone somewhere, it follows that all that grows on the land is owned by someone somewhere, apples being no exception.
While ownership is clearly apparent in orchards with clear boundaries it is less so in hedgerows and wooded areas. No doubt roadside apples technically 'belong' to the Highways Agency, while those growing beside a field footpath 'belong' to the land owner.
It is thus this distinction of ownership that qualifies the production of scrumpy.
If a cider maker buys his/her apples or gains the owner's permission to use a tree's crop or collect windfalls, the scrumpy qualification is lost. However if there is no permission sought and the resulting fruit is turned into cider, it will be scrumpy.
In my opinion this is how the term came about - while scrumped apples are technically stolen apples they are more likely simply 'not missed', in that the landowner does not want them - he's not, or his agent has not, set out to profit from them.
This brings about an interesting situation, in that if he doesn't want them and you do, then so might someone else! Thus the confusion of ownership...
By way of example, I once had a gooseberry bush growing at the bottom of my garden. I should point out that in those days we lived in a long row of terraced houses... One year the gooseberry bush fruited rather well. Now I like my goosberries (delicious in a fool...) just turning yellow and so I decided to give them a day of two more to ripen. Come Friday off I sets with my colander to the bottom of the garden only to find NO goosberries - not a oner - all gone.
It seems someone else preferred them a little greener and whether a neighbour perhaps thought that I didn't want them or the birds got there first, I'll never know.
Thus it is with apples. Some growing locally fall late and as I'm busy dealing with the falling earlies they don't get early attention. One year I got a bit low on sweets and set off with my lettuce trays to find - LO - just one single solitary apple left alone on the tree! Someone had got to them first. It could have been a flock of starlings or it could have been a rival scrumper...