i think those numbers (1:1, 2:2, 2:5, 1:1:4) can vary very quickly. in one \"pressing\", multiple combinations can exist. a different number doesn’t necessarily mean a new pressing.
i believe they indicate what father/mother/son was used for the particular cd. (see: http://en.wikipedia.org/wiki/Compact_Di … troforming)
obviously this isn’t an official, international code. it’s just something used by that pressing plant, for internal use.
but that’s just my interpretation of those numbers. if someone knows more about this, feel free to correct or comment.