I don't know of any published production numbers but I do know from speaking with various current producers of figures in order for a run of plastic figures to be cost-efficient (profitable yet affordable for the average buyer) one must run so many of each mold as set-up to run a mold is expensive.
Simple economics teaches us that with mass production the major expense is in the set-up and preparation (stages already mentioned); once you've done that the more copies you make of an item the less each piece costs per item. That means HaT and other companies must produce many, many copies of each mold to reduce the price of the end product so that it is affordable for us to buy and also make it worth their while to run the mold. THAT number has to be balanced against how many of that item the maker thinks he/she can sell. Doesn't do HaT any good to make a couple million Pommeranian Piccolo Players if five hundred thousand sit on shelves (though I think they'd sell out on pre-orders alone).
Now, remember this, the day of the BIG toy manufacturers such as Marx, Timpo, and even MPC are gone. I would daresay even the old venerable Airfix is a shadow of its former glory size-wise. Having met many of the "giants" in the current industry and knowing what I know of HaT, most folks making toy soldiers today are what we call in the States "Mom and Pop" operations operating out of their homes and apartments. They are mostly folks like us who grew up loving toy soldiers and are now making the figures they wanted to play with when they were kids. I know one who is just starting out who has used his garage as his warehouse and has run sales of his first run of figures to clear space so he can run his set.
The toymaker usually no longer owns the machinery that makes the magic toys but relies on another company to do it for him. That company is usually in China around the globe.
The Chinese company that actually makes the figures has other customers and usually, compared to those other customers the run of figures ordered by folks like HaT, Caesar and others mentioned is relatively small. Therefore often our little guys go to the back of the production guieu or get bumped by a bigger, more "important" order. That and stuff like broken molds (it happens), misplaced molds, artist errors that take time to be corrected, and misplaced or stolen shipments add to the time and delays between announcement of a future set and it getting into our hot little hands.
It does no good to sit in the back seat and ask "Are we there yet?" every five minutes, we will arrive at our destination when we get there.