Do you have a source for that? If so, I would find that significant to have. In my digging, the only known source I could find was the Seki City website. The Seki City website claimed “all” blades were tested and stamped, lending support to the opinion by some collectors that their particular blades are gendaito, regardless of the stamps’ presence. But the website article was referring to showato and the impact “poor showato” were having on the industry. So, it is still possible the testing and stamping was only done on showato. In fact Ohmura, citing the number of Cutlery Assoc. inspected swords, states that traditionally made swords were not part of that tally because they weren’t inspected. Since half of the blades in each survey had no stamps at all, many of them from the Seki prefecture, this could indicate they were gendaito, while the stamped blades were showato. But your version still could be true. Here's the original discussion with Nick Komiya:
"First, is what the Seki City site says about its cutlery industry in WW2. They have a long chronology chart of Seki City history and I provide the full translation of the first boxed section from the original below.
'Blade Manufacturing as Part of the Armament Industry
Because the United States and England adopted China-assisting policies in the early years of Showa, Japanese products were driven out of world markets, shutting off Japan’s exports. Thus the mainstay exports of Seki’s cutlery industry such as knives, dishes and kitchen knives took a huge hit and those producers were transformed into suppliers for the military.
During the war, Seki’s entire cutlery industry got drawn into supplying the military, and sword-smithery was once again a thriving industry. In those days, military swords were called Showa-toh to differentiate them from traditional Japanese swords, but as demand grew, bad quality Showa-toh appeared on the market, becoming a social problem. To counter this problem, the sword dealers of Seki devised a program to assure quality by having the Seki Cutlery Manufacturing Industry Association test all newly produced Japanese swords and stamped products that passed this test.
This quality assurance program, combined with the trainee program at the forge and efficiency improvements coming from specialization and job-splitting of the production process, allowed Seki swords to gain the reputation of being affordable yet high quality, leading to a 90% share of Japan’s entire market supply.
The sword industry of Seki in 1944 consisted of 49 smiths of traditional swords, 200 smiths of Showa-toh and 3,000 Polishers.'
Secondly, although the Ohmura site claims that the Sekiwake 関分 plant under the Nagoya Arsenal adopted the Seki stamp as their acceptance stamp, the code list from 1943 below attributes it to the Seki Supervisory Group of the Nagoya Arsenal, one of a total of 10 acceptance outposts of the Nagoya Arsenal. Note also that "Na" in Katakana was from the Iwahana Plant under the 2nd Tokyo Arsenal and it was the Kanji version that stood for the Supervisory Dept. of the Nagoya Arsenal. 関分 is clearly another mistake.
It is clear from the Seki City write-up that it was the non-traditional Showa-toh that invited the quality test and stamping and the later Sho in cherry blossom is obviously in direct reference to the distinction, "Showa-toh". I cannot imagine why he had to tie it to the Ministry of the Interior. Traditionally made Nihonto made by the 49 smiths were not called Showa-toh.
The site says "All newly made Japanese swords got tested", as if testing was not limited to Showa-toh that ruined the reputation earlier.
The Seki City History book consisting of more than a thousand pages will surely have more details. I just secured a cheap second hand copy of the 1999 issue, so in a few months, I should have a few more facts for you to chew on."
So, as you can see, we still need more information.