Is sub allowed? or not?

[Overnbach]

New member here. I registered just to ask this question.

As the scoreboard operator, is it my responsibility to inform officials when a player reports after the first horn? Frequently, between quarters or during a time out, in the general confusion in front of the table, a substitute will report after the horn, and then just go out on the floor with the rest of the team, and the officials on the floor either don't notice or don't enforce the rule.