When Bishop Grant died in 1778, Bishop Hay became Vicar Apostolic immediately. He, in his turn, set about finding a co-adjutor who could succeed him at once in the event of death or other eventuality. In this way the vicariate would not be “widowed”. The choice fell eventually on John Geddes who was in Spain establishing the Royal Scots College, Valladolid. He was consecrated bishop in Spain and came home to Scotland in February 1781. As it turned out, Bishop Geddes died in 1799 before Bishop Hay, so he had to set about again finding a co-adjutor. Co-incidentally, the choice fell on Bishop Geddes’ successor in Spain, Alexander Cameron.
I must explain Vicars Apostolic to you soon. If I don't, remind me!