It is more likely that Gerruskoger was Jenarong's grandson or great-grandson and the reason for the long interregnum was that there was no need for an Emperor.
However in Gerruskoger's reign, Kargzant and Shargash began fighting which is probably code for there was fighting between the worshippers of Kargzant i.e. the ruling Gamatae and the worshippers of Shargash at Alkoth. It is probably this event that prompted Gerruskoger to become Emperor as the Emperor is the only person who could restrain Shargash.
Supporting this is that after Gerruskoger dies in 18 ST, no new Emperor is enthroned for another seventeen years. Even the Fortunate Succession does not bother to invent a conflict over the succession.