Japanese Cover 1931. 5. 11

Hello all

I have some questions for this attached japanese cover.
The postmark date is 1931 May 11? Nagoya?? It's correct?
Then I found something in back of cover like japanese family mark(yamato??), I want to know if it's really an family mark or nothing.

Best regards

The postmark date could be 1931 (Shôwa 6) May 11, but this stamp design is old enough that it may instead be 1917 (Taishô 6). If the stamp is the "New Die" variety (Scott #129b), then it would have to be 1931. Otherwise, it could be 1917.

I can't read the blurry name of the city in the origin postmarks at all, and my ability to read handwritten kanji is pretty weak, but the envelope was definitely mailed to Nagoya. That's clear enough in both the mailing address and the receiving postmark (6.5.13).

As for the return address, I'm pretty sure that it's somewhere in Nagano Prefecture, but I can't read which city/town.

The stamps look to be old die, so I agree with the previous response that it is 1917.