Norman, i appreciate what you're feeling. I've noticed times when i had multiple cameras going when there was alot going on in life (job, family, etc) - so much to concentrate on i'd just want to go and burn some film - what a lovely escape!!! Unfortunately, i'd forget i had already loaded and partially shot a roll in another camera and viola! i'd add to the problem. Eventually, i got really frustrated with the whole situation on took up crack cocaine..... OK, just kidding, but it did get frustrating.
In fact, i had a camera i had loaded and had some really thoughtful compositions on - i was very careful in metering the scenes, thinking through each frame - you know the drill. However, when i had got the 39th frame i knew something was not right - i had failed to actually load the film in the 1st place!!!! I was sooooo bummed.
From that point on i decided to put the multiple camera thing to an end so i'd take out the film on each camera one-by-one, regardless of what was left on the roll (its only film - i can buy more) and have it developed. One by one i cleared out my cameras (though i didn't have as many as you're currently running!), but didn't reload them. Now, i have 2 cameras going, a 35mm (my Minolta XD-11 and favorite lens) and my RB67 Pro-S.
I can't remember which film i have in my XD-11 (lost the film tab...), but i do with my RB67. I only have 9 frames remaining in the XD-11 and 6 in the RB67 and when they're finished i'll reload when i'm going out (and remember to put a film tab in the holder!!!).