QuietOne:
They used to have a "safety" department at assemblies and DCs that was a euphemism for "security." Some years ago it was merged with Attendants Dept. But the main function was providing guards (usually big brothers) to sit at strategic locations at the access points for the stage, as well as a couple of brothers to walk with the sisters as they carried the donation boxes back to accounting.
There was no instructions for letting anyone unauthorized to talk. Anyone trying to get thru was going to be stopped and removed ASAP. I kinda think the Society is more 'legally' aware now, given that DCs are on them. CAs fall under the circuit, and the instructions, from a legal liability aspect are different - Usually lacking or unwritten for a CA, whereas they are written (there is a manual) for the DCs.
JeffT:
They do have someone following talks during DCs. (Not sure for CAs, but I don't doubt the DO and CO, being familiar already with the talks from rehersals would spot a major departure, or even a small one.) But back to the DCs, It seems, from my experience they had one following behind the stage to assist with cues for demos and experiences. And they also had one back in the chairman's office following, line-by-line, for standards reasons.
A few years ago we had a brother (and older gentleman) who gave out during his talk. The attendants, already seeing him having difficulty, had moved closer, and when he started to faint they caught him before he hit the floor. Another brother, the one following from back in the chairman's office, moved right in and took over the talk. He took over at the very thought the older brother was trying to make and continued from there, even completing the older brother's thought. It was, admittedly, an amazing part of that talk. The audience even recognized what he did.
I had one DC talk that was a verse-by-verse consideration. I relied heavily on an academic commentary to try to gain understanding of the passage, as what the WT had in print about it was rather fuzzy. And my research had a great impact on the talk, yet the talk still held to major WT doctrinal points throughout (This was before, or during, the great awakening). Anyways, when I came down and was escorted back to the chairman's office for "debriefing," the DO, who was the convention chairman (not the bro announcing talks on stage) patted me on the back and kiddingly said, 'you were 9 seconds over.' (He did not know I forgot to start my stopwatch and about halfway looked to see my timing, and seeing it not running, just went with it.) But he also said it was a good talk, 'Sounded like you knew what you were talking about.' The brother folowing the talk was sitting there with his outlines. He just looked at me Not sure what he was thinking, but I guess the DO made his statement, so he was probably outranked and couldn't add any dissenting view.
Take Care