My feeling is...

Always count.

If you dont and 5 comes on and gains an advantage its a T.
If he comes on and doesnt gain an advantage play on and I tell the coach it was my fault we started without the player.

Thats what common sense tells me.. and it feels simple to remember..

Not that I would ever let it happen.. I am too OCD for that.

And at least for me, this whole conversation is pretty much a hypothetical, because you're right, you should always count to be sure.

The situation setup in the case play isn't one in which you can count. It is one in which the team doesn't come out of the timeout and you put the ball in play. In such a case, you have nothing to count until after the ball is in play.

Touche. I meant the lengthy substitution case, but I forgot that there are two cases being discussed in this thread.

With respect to using 10.1.9, that is a case where the Coach is holding the team causing a delay of game situation. Another rule to consider is SECTION 5 RESUMPTION-OF-PLAY PROCEDURE, THROW-INS
ART. 1 . . . When a team does not make a thrower available, after a time-out (as in 7-4-4) or the
intermission between any quarter (as in 6-2-3), the resumption-of-play procedure is used to
prevent delay. The administering official will sound the whistle to indicate play will resume. In
each situation:
a. The ball shall be put in play if Team A is ready or it shall be placed on the floor.
b. The throw-in count shall begin and if a violation occurs, the procedure will be repeated
for Team B.
c. Following a violation by one team only, if that team continues to delay when authorized to
make a throw-in, it is a technical foul.
d. Following a violation by both teams, any further delay by either team is a technical foul.

Effectively this negates how 10.1.9 is to be administered.

IMHO, the delay return of a player (who is not deceiving) is a human mistake that shouldn't be penalized. Think about it, Coach has sent A6 to report to sub for A1 and then calls a TO. During the TO, Coach tells A6 not to go in but A1 didn't understand that they were to return. Why is a T needed for no advantage gained especially if Rule 7.5 lets us play without 5 players and it is not a T.

4 Players Following Timeout = Team Technical
 

Yes, I'm "digging up bones" on this one, this 2017 thread regarding a team caught playing with only four players following a timeout. Reason is, it happened last night and the situation was penalized with a team technical foul.
Without having remembered this thread, after reviewing it I seem to be in the camp represented by Nevada on this one, which concurs with our ruling last night. What I'm wondering is why no one in this thread mentioned the phraseology of the 2007,08 NFHS Intepretation which, in seemingly parallel fashion to the two casebook references involved, justifies the issuance of a technical immediately upon discovery that only four players are on the court following a timeout. That interpretation is pasted below.
Anybody interested in helping me understand this issue more reliably?

SITUATION 12: Following a (a) charged time-out; or (b) a lengthy substitution process involving multiple substitutions for both teams, A5 goes to the bench and remains there mistakenly believing he/she has been replaced by a substitute. The ball is put in play even though Team A has only four players on the court. Team A is bringing the ball into A's frontcourt when the coach of Team A realizes they have only four players. The coach yells for A5 to return, and he/she sprints onto the court and catches up with play. RULING: In (a), the officials shall stop play and assess a team technical foul for not having all players return to the court at approximately the same time after a time-out. The technical foul counts toward the team-foul count. In (b), the officials may permit play to continue without penalty. A5's return to the court was not deceitful, nor did it provide A5 an unfair positioning advantage on the court. COMMENT: Even though neither situation provided A5 or Team A with an advantage, teams are expected to return to the court at approximately the same time following a time-out. The officials should have also followed the prescribed mechanics and counted the number of players on the court, ensuring each team has the legal number of players. (10-1-9; 10-3-3)

Actually saw this once in a game I was part of. We had called a timeout and made some substitutions. AFTER the TO the ball was put in play and we only had 4 players on the court. We caught the situation and quickly called another TO and got our 5th player back in the game.(FWIW it made no difference in the game as we won by 21 points)

Nothing has changed, and I don't think the 2007-08 Interp adds anything that hasn't been discussed.

1) there's a difference between "following a TO" and "following a substitution". We all (I think) agree.

2) There *might* be a difference between "immediate T" (Nevada) and "T when the player returns" (Camron) in the "following a TO" scenario.

Not to throw another wrench in but what if coach Norman Dale's it:

His team is on the floor.

If he doesn't send anyone on the floor we are good right?

Then what is the procedure for subbing a player in later to get back up to 5?