Gerard:
Let's see:
If the stem is at 10:00 o'clock, you are early
If the stem is at 11:00 o'clock, you are on time
If the stem is at 12 noon, who knows.
I always heard 11:00 o'clock too. I just wanted him to put the stem at the highest point on the wheel and see if any calcium chloride came out. It would be filled too full then. You have to leave air space so the tire can flex. I gave up filling tires years ago. I'd rather add external weights. Loaded tires were great for plowing, you filled the tire than was on the dead furrow side. Problem with filled tires is that with any large tire, if you dismount the tire/rim from the tractor, you'd better be Superman or it's going to bust your nuts or your back. Then you have the corrosion problem. Beet juice, washer fluid or external weights are better.
As far as the valve stem being an indicator of whether the tire is tubed or tubeless, usually a tubed tire will have a stem with a retainer nut on it. I said usually, not always.
If your not going to farm (plow). I'd loose the calcium chloride anyway. About the only thing it's good for is dust control on dirt roads.