Other mistake: Either there was or wasn't a 5-year contract from the onset. At first, Sherwood told Bob, "It's just a pilot episode. If we get picked up for a series." Narrator Barry Williams said his agent called to tell him "the network picked up the Brady Bunch for a full season." Season One ended but Sherwood didn't call "until the last minute" to tell the cast they "would be coming back to a second season." Later, Sherwood told Bob that he knew when he did the pilot that he signed a 5-year contract. (00:05:50 - 00:21:40)
Suggested correction: Those two things are not mutually exclusive and that's not how it works in the television industry. Actors usually have to sign a test option agreement with the studio prior to the pilot being picked up (sometimes even before auditioning). This ensures the studio that the actor is committed to the project long term should the pilot be picked up, but signing the contract agreement doesn't guarantee the pilot will be picked up. A 5-year test option agreement seems pretty standard.
I'm aware of such contracts - and surely Florence Henderson would have also been required to sign a five-year agreement, but there (conveniently) was no mention of this.