Conversation so far:
What were the recordings?
Producer Norman Whitfield recorded "I Heard It Through the Grapevine" with various Motown artists.
What other recordings did they make?
The first known recording is with the Miracles on August 6, 1966, though there may also have been a recording with the Isley Brothers.
Did that recording go missing?
a track has not turned up - some Motown historians believe that a session may have been scheduled but cancelled.
Were there other recordings?
The Miracles version later appeared on their 1968 Special Occasion album, and a slightly different take.
What was the next recording?
Marvin Gaye's version was recorded in spring 1967, and is the second known recording.
Was this the most popular recording?
Gladys Knight version was released as a single in September 1967, reaching number 2 in the charts.

Question: What other people made recordings of this song?
Self-contained rewrite: What other people made recordings of Gladys Knight song besides Marvin Gaye's version?