I don't think you ever said how big your coop was?
Run is 8x12 which is a bit tight.
Did the drop off in laying start when the bantam went broody(what did you do about that?) and/or when they ranged less?
They may be reacting to stress.
With those ages the 'math' of number of eggs in your first post sounds right on.
New layers aren't always consistent, some birds only lay a few times a week, not all the pullets are laying.... and the broody may be scaring them away from nests?
....and like @Blooie sez: They're not pez...
How many birds to you have...with ages in months, please?
How big is your run, in feet by feet?
Unless your run is fairly small and bare, they can be pretty sneaky about hiding eggs.
Might have to confine them to the coop to know for sure.
Butt, you can check pelvic points to see if your older...