All the stamps, except the first one, appear to be CTOs.
Scott catalog numbers, with dates so you can look it up in other catalogs.
Row 1
S1: China(ROC) 1271(1960) or similar; genuine postally used; this stamp also came in granite paper variety; granite paper variety also has 2 design types -- 7 lines in "0" of "40" and also 8 lines
Row 2
S1-S3: North Korea 465-467(24Jul1963)
S4: China(PRC) 255(1955)
Row 3
China(PRC -- Northeast Liberation Area) 1L157, 1L157, 1L158, 1L160(1Oct1950)
***based on your picture, all 4 look like reprints; the red-brown should be much "redder", but hard to tell on a monitor; in addition, the paper is nearly fault-free and they appear to be CTOs; there is a better test than the color; from a post by ZhangCheng:
Quote:
for the small flag stamps,a unofficial of China announced way,measure the width of red silk ribbon round the mast(the longer part),0.4mm will be original,0.6mm will be reprint,and there is 0.5mm type,then via the leaves.Or <0.5mm will be original,>0.5mm will be reprint.Not sure for everytime,the flag stamps is the hardest one of China stamps to differentiate Original and reprint.
For stamps that have suffered discoloration (as in your stamps), I would say this is a much better way. But again, they appear to be CTOs and so are very likely reprints.
Row 4
China(PRC) 716,720,717(15Oct1963)
Nice stamps!

k