To dm, I mean. I have had multiple occasions where people get an easy decap or something like that on me or somebody else. And they explain it as multiple hits contributing to DM (e.g. more red parts are easier to DM)

Which I tried in SP by mauling head and shoulder on DM 100 and I noticed no colleration between redness and how easy is it to DM.

Is this total BS about multiple hits contributing or what is it?

Multiple hits do in fact contribute.

If the joint is red, or still rather pickish, dms are muuuch more easier to get.

You might not notice the difference for single dms, but for the huge booms its really helpful.