A Public Speaker does have a certain leeway in preparing his talk. Even when they were 45 minutes long there was more material provided than could be covered in the time , and now they are cut short to 30 mins. One is supposed not to deviate
I have never heard of anybody following the outline to check a speaker. I do not think anybody listens very hard these days
Provided that you do not say anything noticeably outrageous, nothing will be said if a speaker deviates and brings in additional research.
The "Special Talk" every Spring is viewed as more important and should not be deviated from. The words and emphasis though are the speakers own. It is very difficult to read a manuscript like it was a talk , and you would know if he was reciting it.
I believe that Assembly talks are rehearsed before a C/O or someone, but they never gave me one of those