Model designations gone wrong
There have been a few instances over the years where they lost the plot with model designations. I think in North America you may have got more than elsewhere, particularly around the era you mention. You mention the 3.2 in the 300E and 4.2 in the 400E (which we never got down under). Strangely, in Oz at that same time in 1993 our 300E dropped back to the 2.8 (24v). Our 3.2 was a 320E (and 320CE coupe). In Europe, I believe the same cars were, logically, 280E and 320E. The S-class at that time were also strangely 300SE for the 3.2 and 400SEL for the 4.2. We also had a 300E-24 and 300CE-24 to distinguish the 24 valve 3 litre cars from the 12 valve 300E and 300CE.
Earlier there had also been a few odd ones. Some of the 250 got a 2.8. When they replaced the old alloy 3 litre with a 2.8 in the 300SEL in the late '60s it was still badged 300SEL. When the same car got the big V8 it had an additional 6.3 badge. Later the similar 280SE(L) got the additional 3.5 badge (uniquely 4.5 in the US) with the addition of a V8. Whilst our 350SL did get the 3.5 yours got the 4.5 before they decided to badge it 450SL. Some of the late 450SEL got an additional 6.9 badge indicating the larger V8. Some of the late 450SLC got a 5.0 badge before the 500SLC badge appeared.
The 190E series never really got it right. The original had a 2 litre however 200E was already in use on the W123 series so 190E was used. Some (all the 4 cyl. in the US I think) got the 2.3 (of the 230E) with an extra 2.3 badge and some got the six with a 2.6 badge. Later a 190E 1.8 was introduced and in Oz we also got a popular low spec/cost version badged 180E (which did make sense!) to address the problem of the overpriced, slow selling 190E 1.8.
With the introduction of the first C-class around '94 all badging changed to signify the class first then the engine size. A chance to get it right. There were correctly badged E280, E320, E420, S320, S420, etc. This was fine for a while, until the C240 and E240 went to 2.6. The C180 also went to 2 litres. Now we have the strange situation where a C180, C200 and C230 (in the C sports coupe) are all 1.8 and the other situation I mentioned above with the new 3.7 badged 350. Why!
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.