Yeah... There was a box alarm in 20's area yesterday, they put a Baltimore County Fireboat on the call. I have heard it in the past but it kind of rarity to hear Balt County Boats dispatched usually Baltimore City.
I'd heard Boats come across from BCounty over the years but it's rare. On occasion, you'd even hear Queen Anne's boats and even less frequently - Kent County boats.
I suspect, now that the County has come out of the dark age with CAD (dated back to the 90's at least), I think there is more data now shared between CAD systems in some way and CAD can automatically pick up some out of county units based on both their status and now just being in CAD. On the old system, it was more manual.
And since CAD now does things based on distance/travel time to include vehicle locators, dispatches will be different like this....
Not sure how the responders are handling it but when PG implemented vehicle locator / location based dispatching a few years ago, the volunteers were pretty unhappy about it (the Fire Service hates change). Eventually, as with everything new, it all settled down after a while (and folks realized things weren't going back to the way it was).