no matter how thoroughly I searched, i couldn't find those buggers. any ideas where they could've been hiding? and, why was there was no originating airport associated with it? thanks! (screenshot attached...I hope...)
The slot was in SCE. If you did not have any routes that you created but didn't schedule, then the only way to end up with an unused slot is to close a route and un-check the "release slots" box when closing a single route, or by selecting multiple routes in the Manage Routes page and choosing "Close routes and keep slots". The second option is very easy to do accidentally, considering it's a drop-down menu and "Close routes" is immediately above "Close routes and keep slots". I accidentally click on the wrong one frequently, although I usually catch it when the confirmation box pops up.
Once you close a route but keep the slots, those slots are available to you for a new route. It doesn't matter what base you formerly had a route from, the connection is broken when you close the route. If this is the case, then you probably opened a new route from your base to someplace other than SCE using the existing slots and that's why you didn't get a nastygram about those slots at your base. But that SCE slot was still sitting there unused. You could have used it to open a route from any of your bases.
What also may have happened is that you had a route from (hypothetically) DCA-SCE, but needed to reschedule it or move it to a new plane type, closed the original route but kept the slots, then rescheduled the flight on the new plane. But the new plane is either faster or slower, or has a different minimum turn time, and while the departure time was the same at DCA, the departure time at SCE fell in a different clock hour. Even a 5 minute difference can cause this if the old time is 12:00 and the new time is 11:55. Because the old slot was for the 12:00 hour, the system purchased a new slot for the 11:00 hour and left the 12:00 slot alone. Again, this is just hypothetical but it is frequently the cause of phantom slots at outstations.
The quickest way to find if you have unscheduled routes
is to go to the Manage Routes page and click on "Notification View". There is no quick way to find if you have unused slots
at a destination. At your base, on the slot page if you see an asterisk anywhere, you have an unused slot there.