The commissioners will have no say on how Island Transit operates. You'll have to go to their board of directors for that, or a lawsuit. Does the county sheriff have anything to say about OC? What about OHPD? I'm asking because once you get one or more major law enforcement agencies onboard with understanding OC is legal it gives you more standing with the transit agency.
For instance when I was going back and forth with Intercity Transit I got them to admit to the legality of the carry of concealed handguns, and unloaded cased longarms, but I had to show them the Olympia PD training directive on OC (twice BTW, and with two phone calls to even get them to look at it) before they would accept that OC was legal.
FIRST you get Island Transit to acknoweldge they understand 9.91.025. Then you show them every fashion in which it is legal to transport a firearm. They will be that dense.
In Intercity Transit's case they had to back down when I showed them the OPD document. Not only did it prove my point, but they would be the ones called in most cases if an operator didn't like OC. If the cops won't back them on their play, then why bother?
PM me your email address and I'll send you the correspondence I have had with Intercity Transit, it might help you in your cause if you forward it to Island Transit. It includes a letter from the director stating he believes a holstered firearm is considered carried in a non threatening manner or something like that. I also have documents from Community Transit but I'm not sure it properly address OC, I'll have to review that as well.
If you like, I still have something of a bone to pick with Island Transit :P as when I was 19 they kicked me off for a cased shotgun and would never admit to 9.91.025 applying. They pulled some strange thing out that they felt justified their case. In fact you might want to demand any emails from 1999 regarding the transport of fireams on the bus from them just to see what they were thinking then too. So I'd be more than happy to add my two cents to your fight on this one. In fact would enjoy it immensely. It's a bit of unfinished business and the very begining of my own gun rights advocacy.