One of those pieces was Præludium fis-moll (Bux WV 146).
Here, I shall argue that a sharp and a natural need to be added in bars 9 and 10 of the Viderø edition as indicated in Example 1 below.
It follows that the second last sixteenth in bar 9 must be a b sharp, and the middle sixteenth in the third group in bar 10 must be an a natural.6
 Diderich Buxtehude: Nine Organ Pieces Revised by Finn Viderø,
With a Commentary. The publishing company is indicated only in the notice
“Emendations copyrighted. © 1985 Forlagsnr. 549 © E&S”
where E&S obviously means Engstrøm & Sødring.
 Copenhagen University Book of the Years 1968 – 1969 at
says, under Ongoing Activities: “Finn Viderø arbejder med tekstkritiske studier over Buxtehudes orgelværker.” (...is working on text-critical studies of Buxtehude’s organ works). A few lines earlier it says, “Finn Viderø: European Organ Music of the 16th and 17th Century. Wilhelm Hansen 1969.”
The preparation phase for Viderø’s Buxtehude edition can thus be estimated to have lasted for around sixteen years.
(The work had begun earlier: Viderø published an article on Buxtehude problems in Dansk Musiktidsskrift in 1937. Full reference to this and other publications, including those referred to in his foreword, in a downloadable bibliography at www.dieterich-buxtehude.org.)
 Among other things, Viderø reconstructed two missing half bars in
Bux WV 164, starting from the middle of bar 73 (bottom center of page 30 in his edition).
An erratum to Viderø’s edition says, “Bux WV 164 Bar 5. The soprano b 2 should be a quarter.”
Example 2 shows bar 5 as it looks in Viderø’s edition before the erratum is applied: The b 2 is erroneously printed as an eighth. The erratum does not specify how to make room for a quarter, and we will have to figure out what Viderø thought Buxtehude’s intention was.
We can either remove the rest in front of the b 2, or we can remove the dot from the f sharp . Which is best?
If we keep the dot and omit the rest, we get Example 3. It invites legato, which, if taken literally, implies exchanging hands on the f sharp or playing much of the bar with the left hand.
Viderø, unlike many modern players, followed a strict legato tradition; he would have changed hands as a matter of course if he had thought Buxtehude did not intend a rest.
However, I decided to keep the rest and omit the dot for Example 1 far above, because I think that solution agrees better with Buxtehude’s composing style and with Viderø’s playing style as I remember it. Viderø often placed the transition from a tone to a rest exactly on a beat, with rhytmic effect. Bar 5 in Example 1, in which a rest on a beat appears twice in the soprano, offers two opportunies to do so.
(I attended all of Viderø’s lectures at Copenhagen University during 1965-6, took private lessons with him, and often turned leaf during his performances and lectures; but I do not recall how Viderø played bar 5 on the one occasion where I saw him play the piece.)
Josef Hedar included the rest, but wrote the f sharp as a dotted half (Example 4),
implying a total of five voices during part of the bar. Arguably, the resulting chord becomes a kind of
preparation for the chord in bar 7 (Example 1). But in that case – at least in my opinion
– the soprano ought to start moving downwards from a different level in bar 7 than it does in bar 5,
and our seemingly minor issue begins to look like a symptom of a deeper problem.
Indeed, instead of proposing corrections to bars 5-7, Viderø said in his notes,
“At the beginning of the introductory section of 29 bars there are several passages which seem
doubtful as they differ from what is Buxtehude’s usual style, the most glaring example being the
B major six-four chord in bar 5. Also questionable is the sudden and quite unmotivated group of
thirty-seconds on the second beat as well as the peculiar B minor tonality of bar 6 which suggests
that some (how many?) bars have dropped out. This supposition finds support in the entire lack of
development prior to the appearance of the chromatic lines in bars 9-11 which normally would announce
a final cadence of a far more substantial section. Naturally, as it is not possible to reconstruct
the lacking bars the player would do best to omit bars 5-7.”
Perhaps it may be concluded that the piece still has unsolved problems.
 In bars 9 and 11, the melody starts moving down one crotchet earlier in the Viderø edition than it did in the Hedar edition. Viderø conjectured in his notes that an e sharp was notated in the tabulature as f , then (erroneously) transcribed as f sharp. Similarly, a b sharp was thought to have been notated as c and transcribed as c sharp.
 My subjective impression is that the two emendations remove a flavor of randomness from the piece.