I have only owned four W124s -- a 1992 300TE, two 1995 E320Ts, and a 1994 E500. There were definite (but subtle) differences between the TE and the E320 wagons. I am also very familiar with the running changes that were made from 1992 to 1994 on the 500E / E500, and there was some cheapening done during that model's 4+-year production run (1991-1995) that is tangible (the early closed-deck vs. later open-deck M119 blocks are one single example of this).

I also own a 1987 560SL and a 1989 560SEC and I don't see any tangible differences between my cars and those produced for the 1990 and 1991 production years (the final years of those cars), respectively.

What happened was that the Japanese luxury marques (particularly Lexus and to a lesser extent Infiniti [and Acura in 1986]) came on the scene starting in 1989 and it took a few years (after arrogantly dismissing them initially) for MB to actually plan and make production changes mid-series in response to those marques' debuts.

Remember that MB instituted its HUGE price drop for the 1993 model year. I can definitely tell you that that price drop was not planned for back in 1989 when Lexus introduced the LS400 at a price point of $35,000.