One is a capped group on both AI HWs.
One is a capped group of threatfleet (this always produces at least one).
And the third is time-based additions of Nemesis frigates to threatfleet/SF, which I don't think has a cap.
My notes from the AS beta era say you're correct. While some of the exact values may have changed, this should be fairly close.
The AI HW Nemesis fleet is based on Champion count, hull-size, and inverse-AIP, but is capped. AIP over 30 should cause the max to reduce, down to about 30% at 150+ AIP. Pre-spawned Nemesis will no go away, however. They just won't respawn.
Then,
each AI spawns Nemesis frigates equal to:
#_Champions * Hull_size * (Diff / 7.0) * 0.5. For 8 Champion Frigates, this is 4 at Diff 7, 5 at Diff 9, and 6 at Diff 10. Minimum 1.
This count is capped at the listed number, and when killed, they respawn at 1 every few minutes.
Finally, there's the "Counter-Champion Dirty Tricks". AI 1, and ONLY AI 1, uses this. Every minute, the AI accumulates some points based on:
(100 * numberOfChampionsInGame * humanChampionHullSizeFactor * difficultyFactor * lowAIPFactor)
towards Dirty Tricks. Unfortunately, right now the AI only knows 1 trick: Spawn a SF Nemesis frigate by spending 6000 points. My notes do not state a cap.
Diff 7, 1 Champion, AIP 10, Frigate hull: 100 points per minute, or 1 SF frigate per hour.
At AIP 150+, Battleship hull, this'd be 120 points per minute, or 1 SF frigate every 50 minutes.
Worst case gets a little crazy:
Diff 10, 8 Champions, Battleships, AIP 10: 4576 points every minute, or 45 SF Frigate per hour - but the AI is capped at purchasing 1 spawn per 5 minutes.