I bought a set of plates for MC21 dry clutch and got the correct 4+1 fiber plates but I also got 5 steel plates 22322-KV3-780.

according to the parts manual there should be one 22322-KV3-780 and 5 22321-KV3-780 steel plates.

Did the former owner get this totally wrong or could there be a reason to install these plates instead of the standard configuration.

I did f.ex. see that Tyga recommends other than standard plates for the 300cc version.
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Poul
"If Life Gets Boring, Risk It!"
MC21SE, KISS box
MC21SP, HRC box, racing loom

You should have 5 x 2.9mm plates and 1 x 2.0mm plate. The clutch mod, as shown in the Tuning section requires the one 2.0mm plate to be replaced with an extra 2.9mm plate. This will increase the preload on the clutch pressure plate.

By the looks of it you have 5 of the thinner plates for some reason.
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If I have to take the carbs off once more...