Wasn't there a bootleg set of US singles quite recently, which amounted to 6CDs? Wonder if the "16" was a mistyping? I can't see Capitol EMI putting out a 6 CD set.
Found it... the sixth disc was a bunch of promo-only tracks and other slight oddities. (Excuse the formatting - this is a crude tidy-up of a cut & paste). The full line-up is on Bootlegzone.com and yes it does appear to be a fan compilation rathe than a silver disc boot.
Disc 6
1 Add Some Music To Your Day (B. Wilson / M. Love / J. Knott) 3:37
Promotional Single Version
The Beach Boys
(date unknown)
2. Susie Cincinnatti (Jardine) 3:02
Promotional Single Version
(date unknown)
The Beach Boys
3. Tears In The Morning (Johnston) 3:12
Promotional Single Version
(date unknown)
The Beach Boys
4. It's About Time (Wilson/Burchman/Jardine/Wilson) 2:55
Promotional Single Version
(date unknown)
The Beach Boys
5. You Need A Mess Of Help To Stand Alone (Wilson/Rieley) 3:27
Promotional Single Version
(date unknown)
The Beach Boys
6. Cuddle Up (D. Wilson / D. Dragon) 5:29
Promotional Single Version
(date unknown)
The Beach Boys
7. Almost Summer (B. Wilson / M. Love / A. Jardine) 2:31
Promotional Single Version
(date unknown)
Celebration
8. Here Comes The Night (B. Wilson / M. Love) 3:22
Promotional Single Version
(date unknown)
The Beach Boys
9. Hold Me (C. Wilson / M. Smith) 3:31
Promotional Single Version
(date unknown)
Carl Wilson
10. Night Time (B. Wilson) 3:07
Promotional Single Version
(date unknown)
Brian Wilson
11. Somewhere Near Japan (Phillips/Melcher/Love/Johnston) 4:13
Promotional Single Version
(date unknown)
The Beach Boys
12. Problem Child (T. Melcher) 3:44
Demotional Single Version
(date unknown)
The Beach Boys
13. Forever (Wilson/Jakobson) 3:00
Demotional Single Version
1992
The Beach Boys (Wee Helper's guessing the Stamos version?)
14. Forever (Wilson/Jakobson) 3:06
Demotional Single Version
1992
The Beach Boys (likewise - maybe a Euro-remix?)
15.
Under The Boardwalk (A. Resnick / K. Young / M. Love) 3:29
Demotional Single Version
(date unknown)
The Beach Boys
16.
Summer In Paradise (Love/Melcher/Fall) 4:10
Demotional Single Version
(date unknown)
The Beach Boys
17.
Summer In Paradise (Love/Melcher/Fall) 4:29
Promotional Single Version
Concert (date unknown - Wee Helper's guessin' the way-superior-to-the-album version recorded at, I think, Wembley, London)
The Beach Boys
18. Don't Worry Baby (Wilson/Christian) 3:22
Promotional Single Version
(date unknown)
The Beach Boys With Lorrie Morgan
19. Sloop John B (Traditional - Arranged By B. Wilson) 3:42
Promotional Single Version
(date unknown)
The Beach Boys With Collin Raye
20.
The Warmth Of The Sun (B.Wilson/M.Love) 3:15
Promotional Single Version
(date unknown)
The Beach Boys With Willie Nelson
21. Caroline, No (Wilson/Asher) 3:15
Promotional Single Version
(date unknown)
The Beach Boys With Timothy B. Smith
22. Little Deuce Coupe (Wilson/Christian) 2:51
Promotional Single Version
(date unknown)
The Beach Boys With James House
23. 409 (Wilson/Love/Usher) 2:20
Promotional Single Version
(date unknown)
The Beach Boys With Junior Brown