The only answer I can give you (and I was once a banquet server) is that, generally speaking, the only thing the venue gets is the total number of each dish, i.e., if there are 100 people, the venue will be informed that there will be 40 chicken, 25 steak, 20 duck, and 15 vegetarian dishes. They are not notified of WHO will be eating WHAT, nor where each person will be sitting. Also, in most banquet situations I worked, other than the head table, there was no assigned seating per se, but merely open tables. True, there were some events where there was assigned seating, but most were not. Now, with the events that did have assigned seating, they probably could do what you are saying, if the venue was supplied with an itemized list, i.e., Sam Smith has duck, Liz Smith has steak, etc. But I have never seen such an itemized list be provided.
Hope I've answered some of your questions.
"The Customer Is Always Right...But The Bartender Decides Who Is Still A Customer."