'Sealing' is the term used when a will that has been proved in another jurisdiction (eg Scotland) is sent to the English probate registry to be recorded there. There is no need for a further probate in England, as sealing is sufficient.
Sealing in itself gives rise to very little paperwork, and I was once advised by someone in the probate registry that anything I ordered from them would tell me no more than the index does.
In cases like this there will be some kind of grant outside of England, and this should be more informative; where this was might be apparent from the index, but if it isn't we might be able to help you trace it. You'd need to tell us more about your great grandfather - at least his name and where he lived and died.