A pleasure to have helped.
The term "deep stall" usually means an unrecoverable stall, where for whatever reason the aeroplane shows a complete disinclination to recover.
Speaking for myself, I've only ever seen it once, in a canard single seater with a very high thrustline. If you stalled it and left the throttle at idle, there was insufficient nose-down pitching moment to recover - I actually HAD to use thrust to unstall the canard - really quite disconcerting.
Probably the best known case of a deep-stall is the BAC 1-11 which killed a flight test crew when it stalled, but if memory serves correctly the mainplane blanked the tailplane so there was no elevator authority to pitch down. There's a nice explanation of this
here.
G