Example: in the album ROCK AND ROLL FOREVER, lead guitarist Harvey Mandel took care of lead duties.
In a few instances only, our heroes were lacking completely. An example is the infamous ROCKY ROAD album (The New Ventures, 1976).

Interesting note: the album TV THEMES featuring session musician John Hunt for the lead parts this time, appeared in the same year (!) and it seems therefore that it’s no coincidence that both these albums share that same mutual overall sound which really doesn’t sound like the Ventures, to my ears anyway!
There have been NON-VENTURES pirate albums too, such as: THE VENTURES GREATEST HITS (Europe: "Red Dog" releases, or "Black Tulip" recordings, 1988) which didn’t feature the Ventures at all, of course.
To be sure, the Ventures did have their own Greatest Hits albums with many of their past hits which they had re-recorded in 1979/1980 and now published under their own TRIDEX label.
I was surprised however to learn from a previous thread on this forum that the Ventures weren’t present either on their so successful album THE VENTURES play TELSTAR… I find this may be true for only some of the tracks perhaps but upon listening closely you can recognise Don Wilson’s distinct rhythm style on others and Nokie’s lead -surely, at least on Apache, Tequila and Green Onions and Bob Bogle on Bass …and of course not forgetting the Ventures’ hand claps, ha, ha.
For those interested, here’s a recap of recordings up to now, which although published under the Ventures’ name, are found to be definitely NON-VENTURES:
1963 -More (from their album: Let’s Go!)
1963 -Wipe Out (from their album: Let’s Go!) (crappy version)
1966 –From Russia With Love (is from Mel Taylor & The Magics "In Action" album)
1972 -Bondolero (is from Mel Taylor and his group’s 007 album)
1972 -Bond Street (is from Mel Taylor and his group’s 007 album)
1972 -Diamonds Are Forever (is from Mel Taylor and his group’s 007 album)
1972 -Dr, No (is from Mel Taylor and his group’s 007 album)
1972 -Goldfinger (is from Mel Taylor and his group’s 007 album)
1972 -Thunderball (is from Mel Taylor and his group’s 007 album)
1976 -Moonlight Serenade (from Rocky Road album)
1976 -Daylight (from Rocky Road album)
1976 -Temptation, Temptation (from Rocky Road album)
1976 -Superstar Revue (from Rocky Road album)
1976 -The Stroke (from Rocky Road album)
1976 -Step Out (from Rocky Road album)
1976 -Gotta Be Stronger (from Rocky Road album)
1988 -Another Dawn (from the "Red Dog sessions")
1988 -Apache (from the "Red Dog sessions")
1988 -Batman Theme (from the "Red Dog sessions")
1988 -Caravan (from the "Red Dog sessions")
1988 -Diamond Head (from the "Red Dog sessions")
1988 -Lullaby Of The Leaves (from the "Red Dog sessions")
1988 -Pipeline (from the "Red Dog sessions")
1988 -Slaughter On Tenth Avenue (from the "Red Dog sessions") (horrid!)
1988 -Walk, Don't Run (from the "Red Dog sessions")
Note: in 1999 M & I Company published a cd KAYO TAIZEN, under the Ventures’ name. It features 22 vocals by various Japanese artists. (The Ventures didn’t play on it).
Sources: Gerald Woodage, the Internet, cd/dvd inlays and The Ventures book.
Your findings/corrections or additions are welcome!

Paul