The Time Is Out Of Joint -- Erroneous Dates in The Notion Club Papers

One of my many peculiarities is being fascinated by things that go on in the background.  When watching a film, I look at what is going on behind the main characters.  I look at the shops and street signs, or if the scene is indoors I try to make out the titles of any books I might see. When reading, I check into historical events and characters mentioned by the author, I look up books and poems that are cited or quoted.  And I check dates given against the days of the week on which the author claims they fall. 

So, recently I was looking at The Notion Club Papers in Sauron Defeated, the ninth volume of The History of Middle-earth series, and found the following days and dates listed for meetings of The Notion Club. I give them below as written in the text, only adding citations.

• night 54 Thursday, November 16, 1986 (HoME IX.161).

• night 60 Thursday, February 20, 1987 (HoME IX.161).

• night 61 Thursday, February 27, 1987 (HoME IX.173). 

• night 62 Thursday, March 6th, 1987 (HoME IX.222).

• night 63 Thursday, March 13, 1987 (HoME IX.222).

• night 64 Thursday, March 20, 1987 (HoME IX.223).

• night 66 Thursday, May 22nd, 1987 (HoME IX.233). 

• night 67 Thursday, June 12th, 1987 (HoME IX.245).

• night 68 June 26th, 1987 (HoME IX.253) -- no day of the week given, but it is fourteen days after night 67 and thus would be the same day.

• night 69 Thursday, 25 September, 1987 (HoME IX.260).

• night 70 Thursday, 2 October, 1987 (HoME IX.277).

It's Thursday nights, I imagine, because that's when the Inklings met in Lewis's rooms in Magdalen. But I noticed a curious fact when I pulled up calendars for 1986 and 1987. The dates don't correspond with the days.  The dates given for nights 60 through 70 are actually all Fridays, and, what is even stranger, the date for night 54 is a Sunday. 

I checked Christopher Tolkien's notes, but he seems not to have noticed the discrepancy. Fortunately, we can explain almost all of the error by changing 1987 to 1986, when the days and dates for nights 60-70 match perfectly. 

Unfortunately, I cannot reconcile night 54 in this way.  16 November in 1985 fell on a Saturday. The two nearest years in which 16 November was a Thursday were 1978 and 1989.  I have played around with the calendar a little and I am unsure if there can be year in which 16 November falls on a Thursday, followed by a year in which all the other given dates are also Thursdays.

So did Tolkien simply miscalculate?  Perhaps.  Probably even. Yet this would be surprising since he was so meticulous about chronology, dates, and moons, in The Lord of the Rings, and he wrote The Notion Club Papers in 1945, precisely when he was most involved with trying to synchronize the multiple narrative streams of the divided fellowship.  There is also the irony of getting the dates wrong in a story about time-travel, which makes me wonder if the whole error is actually an exceptionally obscure and entirely donnish joke. I like to think so, but I doubt we could ever be sure.