STX MC30/31 and STX SE (Special Edition) MC30/31-CH first appeared in 1994. Both were 7 speed, with SE having shiney smokey grey surface finish and STX being mostly silver. Essentially though, apart from the front mech they were the same components, just with a different surface colour.
In 1995, STX SE was replaced by STX RC MC33 and ran alongside the slightly lower end but also slightly changed STX MC32. This year STX had the 'Cromica Bronze' surface finish on the hubs, brakes, mechs and outer chainring.
STX RC was silver and had more in the way of 'better quality' variations than STX. ie they no longer shared the same components in different colours.
This continued more or less unchanged in 1996 albiet with minor alterations to both groupset's cranksets, STI units and mechs. STX went to MC34 while STX RC introduced MC36.
In 1997 STX gained seperate rapidfire shifters and brake levers, and lost it's 'Cromica Bronze' finish instead going back to silver.
STX RC however saw several changes including the introduction of the 8 speed MC38 rear hub and MC38 rear mech. These were available alongside the older 7 speed option. There were also seperate shifter pods to accomodate the introduction of V-brake levers and a canti option too making the 1997 STX RC groupset options somewhat large.
In 1998 STX remained as a 7 speed only groupset until it was phased out the following year.
A pared down STX RC groupset got the new 4 arm chainset, was available as 8 speed only and both groupsets shared the new MC40 V-brakes and levers.
Cantis and 7 speed options had been dropped completely.
Both STX and STX RC were phased out at the end of 1999.
There are a few other interesting transitional changes which I could go into, but not everyone finds STX or Shimano M-numbers as interesting as I do...
You dont go out much then paul