Is this a vintage Martin mystery?

Just before Christmas, I won a 1920s Martin soprano 0 on eBay. I also ordered the Walsh/King book from Amazon. I received them both the same day! I've been very happy with this ukulele — It's light as a feather, and is louder than my other ukes. Shortly after I got it, I noticed the tuners weren't the ones listed in the book. It should have these Grover 92's...
but what it has looks like these Grover 88’s (but black)...


I'm sure these are the original tuners, because the 92's would've left a footprint on the front of the headstock from the big washers...


Like the 88's however, these tuners have no front washers...


The book allows for all possibilities with this sentence... "Nearly all Martin soprano ukuleles made between late 1927 and the Second World War were equipped with the Grover Simplex pegs of one style or another” — but I was hoping someone may have a more detailed explanation of why/when these 88 (or probably 87 or 89 because they’re black) tuners were used on a type 0.

I have what I believe is a 1934 style 0 and it has the 88 style with front nuts and black buttons.

I've seen those kind. Mine has the "double wedge" like these...

I would post the question on the Four String Farmhouse of the Unofficial Martin Guitar Forum. Tom Walsh writes on it as do a few others who know a lot about these matters.

Minker said:

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44 cents a set...:nana:

With vintage ukes there may be no rhyme or reason.. they used what they had around..main thing the uke sounds good.. enjoy playing and happy strummings in other words, no big thing

You might try the Martin ukulele pics at Antebellum Instruments -
http://antebelluminstruments.blogspot.com/p/museum.html

Thank you for your replies and suggestions! I will post this in the unofficial Martin Guitar forum.