I have this mostly finished PCB where I import a few changes and then ask the autorouter to finish routing the changes only.
I set the "skip routed nets" checkbox, and press Run, and get this answer:
I don't know what Via is set, no changes was made to the PCB:
My expectations was that the attempted count was equal to the count of ratslines at least.
Brand new interactions and interfaces. 
Easy to use and quick to get started. 
