Hello,
This issue was solved.
PRD appears always when there is a difference value enters in MIRO in comparison with the goods receipt, independent of the reason. KDM, instead where there is a variation in the rate exchange between the goods receipt and the invoice registration in MIRO, when the value is equal, minor or higher than the value entered in MIGO up to the equivalent in the conversion currency . Higher than this value only PRD appears.
Hope this will be useful for anyone of you!