I'm quite sure, that the frame is at least 2 years older than the age of it's components. Bitd it was usual in german bike shops that high priced imported frames needed some months or even years to be sold.
After talking to different people who own a lot of custom Rocky Mountains the serial # leads to the year 1991 or 1992. On the last days i searched the internet for every thunderbolt/wedge picture i could find and it looks to me that apart from the serial number of the frame there where 2 things to date a frame.
1st the decalset, old decals = 1989 or older.
2nd the pulleys, it looks like all Rocky Mountain from 1993 or younger don't have any pulleys (front derailleur pulley, rear brake pulley).
So this frame has pulleys and the decalset from 1990 or younger, so it should be made between 1990 and 1992. From the serial number it looks to be a bit younger so probably 1991 or 1992.
I will treat the frame like a 1992, because i want to use the XTR parts from the original setup when it left the shop in Cologne in 1994.