These thin decks were widely distributed from about 1983 to 2000. A Japanese collector has hypothesized that one of the possibilities would be 'Was the stock owned by ARRCO used?' but it is not realistic for ARRCO to have had 'pulp stock' to produce for nearly 20 years.
In any case, I heard from many Japanese old collectors and gained knowledge, but no one has all the USPCC playing cards sold from the 1800s to this year. Finding the thinnest USPCC deck requires the cooperation of cardistry, magicians and collectors around the world.
For example, decks produced in 'International Playing Card Company' were used in many promotional decks, such as orders from universities, companies, and individuals. Many of them were smooth finish and even without embossing, but they were thin, so I remember the quality was high.
Some of these small lot production decks may no longer exist because they are now gone.
Mr. Don Boyer, what kind of deck is the thinnest one you've ever seen?
As long as it is a general commercial product other than a magic special order product, it is OK if it is not made by USPCC.
The absolute thinnest deck I've ever seen was exactly that, a specialized deck manufactured for use by magicians. It's the Phoenix Double Decker - two decks in a tuck box the same size as a standard tuck box. The cards are half the standard thickness - and they're marked and have a one-way marking on the backs. They're available from the producer, Card Shark, at
http://card-shark.de.
Sorry to hear about your wife - I hope she recovers soon and your child is OK.
The device you're using in your photos is similar to a micrometer, but a good micrometer, digital or analog, will give you increments of 0.01 mm. Your device looks like a caliper - a simpler measuring device, not as precise as a micrometer, which is technically a type of caliper.
Measuring the thickness of a single deck will NOT give you an accurate measure of a deck's thickness - as odd as that sounds. The issue is that the thickness of the pasteboard used to make playing cars is NOT of a uniformly consistent thickness. There can even be variances of thickness among cards within a single deck. Simply put, as careful as a manufacturer may be in the creation of its paper and pasteboard made from that paper, it's not done with only a limited amount of precision, allowing the thickness of a deck to be just right to fit in a box of cards - but there's a lot of "wiggle room" within that standard. So measuring one deck in a print run and measuring another deck in a print run, odds are that if you're measuring to a certain degree of accuracy, you'll reach a point where very few of the decks are precisely the same thickness, but that the overall print run will be within a certain range of thicknesses.
It makes little sense to obsess that much over finding the thinnest deck out there when there's so much irregularity in their manufacture. You could declare that "Deck X" is the thinnest, then I could find a "Deck X" that's thicker, one that's thinner, a "Deck Y" that's thinner, etc. It's like expecting a plain, common spool of rope made from twined strands to be of a uniform thickness for its entire length, when the twining of the strands makes such a degree of uniformity impossible.
Now, you CAN find a deck that's generally thinner in its print run, you can find a deck that's generally thicker in its print run, but not one that's uniformly thinner, especially since there are relatively few stocks used by each manufacturer. USPC makes two kinds of stock, "standard" (mostly used for Bicycle) and "casino grade" (mostly used for Bee), and each of these stocks is available in a "thin crush" version, whereby they press the stock with more pressure between the rollers when binding the two layers of paper with the graphite-infused glue in-between. The biggest issue that they run into in terms of consistency is that they don't make that paper - they make the pasteboard from the paper, but the paper itself is produced by paper mills and they order it from them - and they don't have as much control over that paper. There's also regulations that require a certain percentage of all newly-manufactured paper to have a certain amount of recycled content, especially "post-consumer" recycled content, which has a much worse consistency and shorter fibers.
They're not the only company that runs into such issues, I'm sure.