Jesus, 10 to 20 thousand seeds per plant? That's gotta be a 15 foot outdoor sativa...
How 'bout for your average 3ish foot indoor plant with a fairly decent pollination? What's one looking at, on the upper and lower ends for a plant that size?
getting a couple hundred out of a plant is pretty easy. I also see thousands being possible if you fully pollinate the entire girl in full bloom. Never wanted to do that myself because it would take me too long to test thousands of seeds lol.
Five thousand would be a reasonable number from an average 6 -7 ft. Sativa dominant plant that's been naturally pollinated by a nearby male. ( Just as the female grows in stages, producing more and more pistils, the male produces and releases viable pollen at approximately the same rate. )
Realistically, the folks who grow monster plants ... the 1 lb and over yielders ... aren't about to expend the time and effort needed to do these "stunt grows" and deliberately leave a male standing around to pollinate it. Even if they did, they couldn't be certain that some of the pollen didn't come from a different male, or neighborhood ditch-weed.
Indoors, small plants can produce prodigious quantities of seeds quite easily. All that's needed is a small oscillating fan to blow over the male, towards the female. A 15 inch tall "bonsai mother" in a one gallon pot can produce 400 mature seeds before being clipped back and re-vegged.