If Sausalito tapes were ruined, why there are so many bonus tracks?

[Villavic]

I don't understand what Mick tells in his book about the Rumours sessions. For those who have read Ken's book, does it coincide with what he says about the Sausalito recordings? See:

Then there was Jaws. This was a nickname that we gave to a tape machine that acquired an appetite for eating (and destroying) fresh takes. And yet there were some triumphs in all this. I vividly remember the night Stevie cut "Gold Dust Woman." We'd been in Sausalito for a month, and were beginning to get urgent phone calls from Warner Bros., who were wondering how we were doing. We didn't want to tell them that we were beset by romantic turmoil and that the only thing holding us together was a thread of Mac family cohesion. For me it was Stevie, physically the most fragile of us all, who exemplified the drive to create and prevail. I recall that she did her first vocal track of "Gold Dust Woman" in a fully lit studio. The song needed both a mysterious power and a lot of emotionality. As take followed take, Stevie began to withdraw into herself, reaching inside for the magic. The lights were dimmed; a chair was brought in so she could sit, saving her strength at three in the moming, and she wrapped herself in a big cardigan sweater to ward off the predawn chill. An hour later she was almost invisible in the shadows, elfin under big headphones, hunched over in her chair, alternately choosing from her supply of tissues, a Vicks inhaler, a box of lozenges for her sore throat, and a bottle of mineral water. Gradually she gained total command of her song. On the eighth take, exhausted but exalted, she sang the lyric straight through to perfection.
....
.....
Exhausted, the torn and frayed members of Fleetwood Mac filtered back to our homes in Los Angeles and took a few days off. When we gathered again to listen to the tapes of the work we'd done in Sausalito, we were aghast at how awful they sounded. The tapes sounded... strange. We tried switching speakers and then switched studios, but they still sounded bad to us. It was suggested that the cursed "Jaws" tape machine had somehow ruined them, and deep depression set in. For a while it looked like we were going to have to start all over again.
Then someone found a mixing room in the Hollywood Boulevard porno strip where the tapes sounded . . . well, good enough to work with. It was there, between sleazy "heaters playing films like Dick City and Squirm, that the new album was molded. All the Sausalito tracks were stripped down to the drum tracks and we started to dub new instrumental parts and vocals.

So, I'm understandig that the Rumours album we listen came mostly from the LA sessions. And I guess they re-recorded just the final versions in the way they agreed. If the Sausalito tapes were "ruined", how we got the 2 additional tracks of GDW in the 2004 Rumours deluxe cd? and the rest of bonus tracks? and the early takes in the 2013 expanded release? Does Ken explain this more detailed in his book?