Brian left the tour of his own accord in December, 1964 and didn't return for 15 years and only sporadically since them. Mike wasn't given credit for co-writing most of the hits by Murry Wilson. The only way to get rightful ownership was to sue. Brian would have probably agreed to add him as co-writer but it has to be done in a court of law due to BMI, ASCAP, etc. considerations. Apparently, you do not know what you are talking about.
What are you listening to right now? In My Room recorded by Tammy Wynette