It seems like there is a maximum total number of cars defined for each activity generator template. If that is true, it would seem this is defined in or as part of the .act file, but I cannot find anything in the file that would have this effect.
I say this because various methods of adding rolling stock to the .act file seem to have the same result of the same number of wagons added to the activity, with the extra wagons after the total limit defined as not having matching pickup events and not being used by activity generator.
I got around this when working on the Fonda Johnstown & Gloversville template, by adding pickup events for each siding. That made activity generator recognize all the rolling stock present in the .act file. But I don't understand exactly why this worked. Or why it was necessary (the instructions would seem to imply it isn't).
Now I'm looking at adding cars to the NEC4 template. There are a great deal more sidings and making pickup events for each one is feeling daunting. In theory, this shouldn't be necessary, right? And yet it isn't working to just add cars to the .act file beyond the limit.
I'm doing all of this in a text editor as I no longer have the ability to run MSTS, having upgraded to Windows 8 (and with the FJG route I couldn't get the activity editor to run without crashing anyway).
Christopher