Ahh-ha !!! Thanks for that. Having seen a set of each interchange on a Webley MK.VI, I had convinced myself that all Schofield ones would interchange, too, but I now realise that this is clearly not the case. Thanks for the heads-up.
The confusion crept into my psyche as a result of my proven, tried and tested observation that Schofield BB shells and Webley MkVI BB shells most definitely are interchangeable (notwithstanding the writing around the lip, these two shell types are identical), so I assumed Schofield BB and Schofield pellet shells would follow the Mk.VI model, too: clearly not all do.
Now, what is it that they say assumption is the Mother of ???