Hanyoung,
welcome to the NMB forum!
To answer your questions:
1) Generally, yes, but probably not in this case. These blades all appear to be not very old to me
2) Not really. The 3rd blade (from top) is not necessarily a Japanese one. The NAKAGO surface is unusually uneven so there is a doubt
3) the NAKAGO have been ground "clean" so if there was a MEI before, it might have been visible or ground away
4) There is a sales value in these. As explained above by Rohan, they are bought for research purposes or by knife-makers in the West to use the material.
The regulations in Japan say that no unregistered blades above 150 mm length are allowed to wn, so when police confiscate blades, they are being checked by experts to see if they are historically important or valuable. Then they are cut with less than 150 mm cutting-edge length and given back to the owners.