Two controversies regarding the recording sessions:

1. Organist Al Kooper has repeatedly insisted in interviews that the Nashville recordings were completed within a single set of sessions spread over a week to ten days.  He says he recalls making only one trip to Nashville, and that the claims of a second series of dates must have arisen from latter-day amateur researchers not understanding the studio logs.  For example, an entry for an engineer running off an acetate of one of the songs could have been misinterpreted as a recording session.

It is difficult to understand how two trips from New York to Nashville could have been conflated in Kooper's memory into a single trip (or alternatively how a single trip of nearly a month could be remembered as lasting only a week to ten days).  Nonetheless, plenty of other evidence does support the notion of two separate sets of sessions.

• Michael Krogsgaard, the Dylan researcher who has published the most comprehensive documentation of Dylan's recording sessions (see www.punkhart.com/dylan/sessions.html), was given access not only to the studio recording diaries (where a confusion between a recording session and an engineering session might conceivably have arisen), but to numerous other sources which would have linked a song to its recording date, including CO Cards, Artist Cards and musicians' contracts. For an explanation of these, see the first of Krogsgaard's series of articles via the link above.
   
• The 1970s Japanese edition of Blonde On Blonde (40AP 274-5) contained a booklet which gave the recording date for each song.  "One Of Us Must Know" is correctly given as Jan 25; of the Nashville-recorded songs, five are given as Feb 14-17 while the remainder are assigned to either Mar 8 or Mar 9.  These dates, which presumably came from Columbia in the US, broadly agree with Michael Krogsgaard's reporting of the studio records.
   
• The booklet in the 2010 box set The Original Mono Recordings gave the recording date for each song; while these didn't agree 100% with the dates reported by Krogsgaard, nonetheless they again indicated two separate groups of Blonde On Blonde sessions in Nashville, in February and March 1966.
  
• Original Columbia documents relating to the release of Blonde On Blonde are reproduced in the CD-carrying book of The Cutting Edge, Collector's Edition, and these clearly show the songs as having been recorded at two separate groups of Nashville dates, February 14-17 and March 8-9.

• Dylan's known tour schedule for early 1966 has gaps which coincide with these dates in February and March, but includes numerous concerts in between.

2. There has also been some disagreement as to whether guitarist Robbie Robertson was present at the February recording sessions, and, if he was present, whether he actually played on any of the recordings made.  According to Al Kooper, Robertson was in Nashville the whole time Kooper was there; but, as seen above, Kooper seems to have merged the two sets of dates in his memory.  Robertson himself, in his 2016 autobiography Testimony, makes a convincing case that (1) there were indeed two sets of recording dates in Nashville, and (2) that he was not present at the first set.  Indeed, back in 1966, Charlie McCoy had said in an interview for the October edition of Hit Parader that “The second time Dylan came in he brought his own guitar player with him - Robby Robertson.”  There is furthermore no mention of Robertson in Michael Krogsgaard's 1995 documentation of the personnel for the February sessions.*  Robertson's absence from the first set of sessions has now been confirmed by Daryl Sanders' 2018 book on Blonde on Blonde., which cites further clear recollections on the matter from Robertson.^†  Sanders also clears up another mystery regarding Robertson's involvement: the matter of who played the lead guitar on "Visions Of Johanna", recorded on the first night of the February sessions.  Most Dylan fans had always taken this to be a prima facie example of Robbie Robertson's distinctive playing style, and therefore evidence that he was in fact at the February sessions.  However, Daryl Sanders tells us that the guitar part was in fact played by Nashville session guitarist Jerry Kennedy, who happened to have arrived at the studio in time to play on this song.  So this now appears to be a closed case: Robertson was not there.

^* www.punkhart.com/dylan/sessions-2.html

^† That Thin, Wild Mercury Sound: Dylan, Nashville and the Making of Blonde on Blonde, Chicago Review Press, 2018, pp.127-128