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After the convertible returns calculation process checks the MFP_CONV_CALENDAR override column at the same time that the other override columns are checked:
If the MFP_CONV_CALENDAR column is populated, then use that business calendar for convertible return calculations in conjunction with any applicable System Parameter settings used for convertible return calculations. In this case, this calendar is used in place of any selection in System Parameter 15. The calendar specified in the MFP_CONV_CALENDAR is used to adjust the baseline derivation of the conversion date.
If the column displays NULL, then proceed with current convertible returns processing and apply all applicable System Parameter settings, including System Parameter 15.