Hello Averil,
There seem to be gaps in the Maughold parish register, especially during the 1600s, with several marriages and many baptisms not appearing.
I couldn't find another marriage of William Corkill to Margery, unless it is entered as Margaret (other Margery was recorded at least once as Margaret), and the mother wasn't given on early bapts (to find first wife).
I also have a question mark over "CR has Daniel Corkill [3rd son of Jon d.1669] marr. Margaret Karran 1668; d.1690; at least 2 children William & Katherine" because this Daniel was of Balagory (not Ballajora) in his will, and it was written very clearly.
About the missing wives, their wills were usually under their maiden surname in the 1600s, so unless we can find wills with her children's surname given as Corkill, or unless they were included in a contract, they will be hard to locate. Several wills referred to goods or money " that was due to him by the Death of his mother" (without naming her).
Sue