Java Edition:Sand in Unnatural Position
Sand could not be placed from Classic 0.0.19a to Classic 0.0.19a_06 which made sand in many positions where it does not naturally generate discontinued. This is recontinued in Classic 0.0.20a.
Obtaining
In Classic 0.0.19a, Notch added the hotbar to the game. There was not enough room for all the blocks and so he left cobblestone and sand off the hotbar. This means that the player cannot place any sand until the inventory is added in Classic 0.0.20a (Classic 0.0.20a_01 is the first archived version after Classic 0.0.20a, which is missing).
In a newly generated world of Classic 0.0.19a_04 or Classic 0.0.19a_06 (all other Classic versions are missing in the version range where sand is missing from the hotbar), sand only generates at sea level (y=31) next to water at a depth of 1. The player can make sand fall to reach lower y-levels in these versions by breaking the blocks underneath it (an irreversible action) but cannot make the sand increase in y-level.
This generation means that sand above sea level (y>31) is discontinued. Also, more than one sand block in the same column of the world is discontinued. Both of these configurations can be made by placing sand from Classic 0.0.14a (sand added) (Classic 0.0.14a_08 is the first archived version after Classic 0.0.14a, which is missing) until Classic 0.0.18a_02.