After all this focus on the cards themselves, I started wondering, how were they filed? I noticed that the text in the center of the USAAF IARC's used the term "Kardex":
Attachment:
File comment: Individual Aircraft Record Card – 41-39274 – Center
Individual Aircraft Record Card – 41-39274 – Center.png [ 65.96 KiB | Viewed 2578 times ]
and the bottom right corner read "Remington Rand":
Attachment:
File comment: Individual Aircraft Record Card – 41-39274 – Corner
The answer, as evidenced by the above is apparently in storage cabinets by Remington-Rand:




(Source:
WorthPoint)
The trays then slide out to reveal a tray that holds flip cards:

(Source:
PicClick)



(Source:
Vintage Office Supplies)
One
listing for the "Victor" system even calls it a "Fleet Maintenance Record Card Holder":
Attachment:
File comment: Victor Kardex Visible Book Fleet Maintenance Record Card Holder Vintage
Another shows a card, still in the original holder, that looks strikingly similar in style to an IARC/AHC:

(Source:
PicClick)
EDIT (21-07-27): An advertisement on page 608 of the
Aircraft Year Book for 1944 confirms the widespread usage of the Remington Rand "Kardex Method of Visible Record Control" and its "Graph-A-Matic signaling system". No less than 28 major aircraft and parts manufacturers are named as employing the system.
EDIT (22-06-13): Interestingly, even with all of the computerization of the modern era, there is one place record cards continue to be used in substantially unchanged form: libraries. Among other things, Brodart still sells a product they call "
Daily Periodical Record Cards" which look remarkably similar to aircraft history cards.
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