I note WR45 has a lower case number visible in Master Book, so clearly at least that high were in play when yours was cased.
I can also prove the engraving/dial/hands change theory.
A niggle, here. I believe the new nomenclature came in early 1924. Most (i.e. Straps) are matching by Q4 1923, but...
-9/1923 we still see Square 36 (Wristlet WG18)
-11/1923 we still see Square 35 (Wristlet WG 20).
In 12/09/1923 NYT, we still see Square 31. Described in ad as, "Ultra quality or solid white gold; $30 to $55, according to case and movement." This model does not exist in the Master Book as a solid gold model. At least in my viewing, it has been replaced by Wristlet WG19 (visible differences: numerals, "Gruen" placement, hands, possibly lugs). I have also not found it within the WR section, but I have traced its transition
On 5/4/1924 NYT, the nomenclature is changing. But not yet ours. WF19 anyone? "White gold reinforced. 'Precision' quality."
On 5/18/1924--same electro as 5/4/24--the nomenclature is correct to ours. But at least the engraving, dials & hands, possibly the lugs (and possibly all) have been updated in our Master Book for a final WR19.