You got the papers ready? All those excise labels and stuff gotta be just right.
Cut content from the S.T.A.L.K.E.R. series has been observed since the demonstrations of some of the earliest Builds of Oblivion Lost, the game which would later become S.T.A.L.K.E.R.: Shadow of Chernobyl. Items would appear in one build or demonstration, only to be subsequently removed in later editions. This trend continued during most of development, up to and including some of the latest pre-release builds.
With the release of Shadow of Chernobyl and the official Software Developer's Kit, users were able to examine the game's code and resources in detail. This led to the discovery of a surprising amount of unused and "removed" content, some of which had not been seen in demonstrations of pre-release builds. Similar software was developed for pre-release Builds, yielding even more content.
Following Shadow of Chernobyl, both S.T.A.L.K.E.R.: Clear Sky and S.T.A.L.K.E.R.: Call of Pripyat have also included some amount of partially removed content. Generally, the amount of removed content still present in game files has decreased with each iteration of the series.