In my experience this question typically concerns the handling & performance validation tests.
From the European prospective appendix 7 to ACJ No1 of JAR-FSTD A.030 explains how this situation could be addressed where there are validation data issues that need to be resolved between the Simulator Operator and the Regulator.

This appendix would be equally applicable to devices that have 'grandfather' qualifications and where Simulator Operators are seeking an upgrade of the device. (see also TGL 10 to JAR-FSTD). A similar philosophy and appendix exists for rotary devices in JAR-FSTD H.