Etching and aquatint can be used to produce over 100 prints if required and some artists will employ professional printmakers to make their editions. Other printmakers prefer to undertake the whole process themselves in which case the editions are usually much smaller. The number of the edition is usually pencilled below the corner of the print so 4/20 would denote the 4th print in a series of 20. In large editions, the quality of the print will deteriorate so that the early prints are considered superior. In an edition of 20 this is not significant.
Prints which are taken before the final state of the plate or which are experimental are known as "artists proofs" sometimes market AP or P in the corner

A Professional printmaker will aim to make each print identical but I am afraid that I would get rather bored doing 20 prints all the same so I usually make small changes to the inking process for each print so no two are exactly the same.

Many so-called limited edition prints are simply reproductions of paintings produced digitally with no input from the artist. These are often huge editions of several hundred and should not be confused with a limited edition produced in a traditional manner by the artist himself.