The very nice C6 set, 1st Anniversary of Founding of PRC 1950, the set with the Chinese flag, may be the one that is most prone to intentional or unintentional misidentification. And with reason! The original set will sell for some 200 dollars mint and 50 used, while the reprints yield only around 8 and 3 dollars. The North-East issue is even more valuable when original: 600/800 dollars mint and around 350 dollars used! Reprints are worth only 10 dollar mint/3 dollar used. Thus it is very important to know if you have originals or reprints... But that's not an easy task.
There are four small stamps and one that is much larger. The larger one is the easiest one: look at the big star in the flag: the dots forming the shading are set at a different angle.
All original stamps in the set have a slightly darker colour than the reprints. The letters are thicker with the originals, thinner and less well defined with the reprints. Most catalogues say that you have to focus on the red ribbon around the flagpost and the leaves. The ribbon is darker red and has more square curves with the originals. Leaves are reddish brown with originals, grey-brown with reprints. Even with originals and reprints at hand those differences are difficult to see. I think the combination of the darker colour and thick letters is the best way to distinguish them. The stars in the smaller stamps have more straight contours with the reprints, too, but again: hard to see. Or use UV: originals light up, reprints don't. And used stamps: almost always light CTO, often only in the corner, with reprints, while originals have black, smudgy cancellations that cover large parts of the stamp. As for mint stamps for sale advertised as originals: only detailed pictures will give you some sort of a guarantee, but buyer beware!

Left: Original, Right: Reprint. Notice the darker colour and the lighter folds of the original stamp.

Leaves and ribbon of original and reprint. The colour of the leaves doesn't really show up in pictures, it's much more obvious when you can examine them.


Angle of dots on the large stamp, not really visible in pictures.