GREAT item indeed ! Some comments:
It looks like there's some confusion with regard to the Item Numbers ... Item 932100 should either read 9321000 OR 93210 (7 OR 5 digits).
Item 93205 > Basic Instrument Set, Case, Empty, is a component of Item No. 93200 (Basic Instrument Set, IWIS item)
Item 93212 > Basic instrument Set, Case, Empty (1942 Model), is a component of Item 93210 (Basic Instrument Set, 1942 Model)
BOTH items are listed in the 1942 Medical Department Supply Catalog, and have of course different contents (listed as well as in the 1943 MD Supply Catalog).
The 1944 Medical Supply Catalog still lists Item 9321000 (Basic Instrument Set, Complete, 1942 Model) and Item 9321200 (Basic instrument Set, Case, Empty, 1942 Model), although previously designated an item of the IWIS category (1942).
Based on the colors of the different parts, it looks like the basic case (with maroon-colored straps) was manufactured in an earlier period, while the inserts in khaki were most probably made in 1942-1943 ... there's no longer a trace of Item 93205 !