Complex sentence: He bequeathed a total of 13 works, mainly by Canadian sculptors, to the institution; not all of these are within the remit of this list, as some are situated indoors or in the adjacent borough of Camden.
Split into simpler sentences: He bequeathed a total of 13 works, mainly by Canadian sculptors, to the institution. Not all of those works are within the remit of this list, as some are situated indoors or in the adjacent borough of Camden.