Hi Ronan, I'm not trying to argue that your flag is from the 1950s. I'm just saying we have no info (yet) to place a date on it. People post yosegaki on here almost daily, and maybe 60% of them are obvious fakes. Of the remaining 40%, I'd say maybe a third of those have the hallmarks of a pretty decent yosegaki; addressee, addresser, location, date, signatures of various people who signed the flag before it was presented, etc.
This means a good portion of the flags get thrown into the "not clearly fake, yet not convincingly authentic" pile.
After the war you had some very hungry and desperate ex-Imperial Japanese Army guys who discovered that they could sell wartime souvenirs to American GIs for cash, and so a lot of flags ended up in GI hands this way. When they ran out of authentic flags, they discovered they could fabricate WW2 souvenirs, and the Americans couldn't tell the difference. Nowadays the fakes come from China, where the cost to produce these is, say, a dollar or so.
Which means one ends up looking at these things with a very critical eye. The one in the picture you attached in your post #8 has the recipient's name on it (not to mention it comes with a vintage photograph), so already it has one of the hallmarks of a genuine flag, even if we ignore the WW2 army guys holding it up. I can't read all of it, but it looks like two patriotic slogans to the right side, then the writer's (presenter's) name under that. So there is no need to doubt the flag in the picture.
Your flag has a patriotic slogan, then several lines of unidentifiable text. Hopefully there is a clue in that text that will help educate us as to whether or not it is authentic or a fake. Right now, its too difficult to read so it seems premature to nail down a date for this.