Hi 62aclubworld,
Welcome to Flyertalk and a Happy New Year, it is good to have people on the board with a vast amount of experience on BA, I believe the combined experience of everyone does help. Where have you been the past 9 years?
In your post I can not see what class you travel in or how big your group is. The rules are pretty clear, gold card holders can invite one guest, silver card holders have access to the business lounge. If your group is too big, which it seems it was, there is no complaint as the lounge staff followed the rules. If they did not folow the rules and denied access for a wrong reason I am sure many on this board would have sympathised.
Signing in guests is your perogative, you and a +1 can enter no matter what the definition is of the +1, as long as he/she flies on BA that day.
I personally feel the soft approach works best, if I am somewhere very regularly I try to be friendly with the staff, try to remember their names so they remember me as a trouble free pasenger. When the time comes I need an exception I would ask beforehand if for example next week I could have an exception. 9 out of 10 times that works and when the answer is no it is clear and will not cause trouble on that day.
Globalist