It could be but as you can see Guts and company needed a ship to travel to elfhein island because it so far away unless they didn't want to travel by land on the road that my tough anyway but who know?
Yeah that is the trick as well, maybe they are heading to a port or something? But I think Griffith's army has other ways of transportation, like flying monsters to get to any island easily. It is more likely that Rickert wants to join in with Guts and see how Caska is doing.
Another tough went Gut and Nosferatu fight in from off Griffin Nosferatu destroyed the cave were rike and the little girl were living and maybe went ganisha died those monster's that appears maybe reach the place were rike and the little girl were living but since the cave that protected from evil spirit's was destroyed they were force to let the place
Maybe the opinion like make them travel along with Guts and company, or Griffin army invading elfhein island before Guts arrival,
Anyway I tough someone said miura was oready making the elfhein island charters but this last one don't look like elfhein island charter's even it the name of this last one charter have the name