Shackleton's Onotos - with "patent self filling pen" imprints in 1921?

[KLscribbler]

Recently, I came upon some photos of Onotos formerly owned by Ernest Shackleton. It seems they have not been shared on FPN before, so here they are:

The first one is from a Christie's auction in 2012 (picture can be magnified by clicking on it) :
https://www.christies.com/en/lot/lot-5605380

 

The second one, which looks so similar to the one above that it may be the same pen, is pictured in an online exhibit made by the Osher Map Library of the University of Southern Maine. Scroll down to item no. 67 on this page and you'll see it (picture can be magnified by clicking it) :
https://oshermaps.org/exhibitions/to-the-ends-of-the-earth/section-7

 

If the pens above are one and the same, I wonder if it is currently in the collection of the Osher Library. (Any FPN folks work there, perchance?)

In any case, here is a third one, obviously not the same pen as the above, with much more barrel wear but less discolouration. This photo is from an earlier Christie's auction in 2001. Unfortunately, the photo of this pen is lower resolution than those above. Moreover, the imprint is worn down and quite hard to read on this one:
https://www.christies.com/en/lot/lot-2778060

 

All of the pens are engraved on a barrel band with Shackleton's initials and the year 1921. It seems he must have obtained them shortly before embarking on his final expedition; perhaps he even carried them aboard the Quest. Now, both (or all three?) of them are typical 1920s hard rubber Onotos in most respects - the shapes of the sections, caps, and plunger knobs; the chasing pattern; the absence of an over-under feed. But interestingly, they all bear this style of imprint:

"ONOTO"
PATENT SELF FILLING PEN
DE LA RUE, LONDON

 

The imprint on the last pen is so worn that I can't tell for sure that it isn't the "Onoto THE Pen" type of imprint instead, but based on what I can see, and word placement etc., it seems reasonable to say that it was most likely the same "patent self filling pen" imprint.

I've always assumed the "patent self filling" imprint was early; certainly by 1921 I would have expected to see "Onoto THE Pen" imprints, especially on pens with the newer design of section/cap/filler knob. Clearly my assumption was wrong. That said, I don't have Steve Hull's Onoto book, so I don't know what the best of current knowledge is regarding when the imprint change happened. (Does the book say anything about when the redesigns and imprint changes happened for N and O model Onotos?)

In any case, these are pens that accompanied the great explorer in his last adventures. It is heartening to see them preserved till the present day in such a fine condition.