The
S2 set Gymnastics by Radio (we indeed had something like that in the Netherlands too in the 1950's) is very well known and consists of 40 stamps in all that were printed in se-tenant blocks of 4, so 10 blocks in all.

A complete
reprint set in blocks is worth some 20 dollar mint and 14 dollar used.
Originals carry a high value: a complete mint set will set you back at least 1000 dollar, while a complete used set has a value of around 700 dollar.
So you really want to know if you are dealing with the ''real' deal!
Almost everything that is offered for sale concerns reprints, mint or with CTO-cancellations (that often carry a date in 1955). Used originals can creep up in mixed collections, but I think they are quite rare.
DIFFERENCESThe main difference between originals and reprints concerns the
paper:Very thin in originals: on the backside the design is clearly visible. Paper is light grey in colour. Another difference: The colour of some shades is somewhat different from those in reprints. Design is clear vs. somewhat smudgy in reprints.
On the backside the paper of originals appears so thin that the design is visible. Notice the light grey colour of the paper vs the smooth white colour of reprints.Reprints have far thicker paper that is smoother and whiter.
Notice the different shade of the original at the left side.
Originals (lower stamp) have clear lines, reprints are somewhat smudgyIt is very hard to distinguish originals from reprints just by way of pictures. You really must have them in your hand, feel the paper and look at the backside.
Reprints are often offered for sale as originals, so beware!