How to apply PUM incrementally during upgrade

We are performing an upgrade from FSCM 9.1 to 9.2.19. After the Initial Pass we will be at we will apply PUM to be at PI 9.2.20.

There will be almost 4 PeopleSoft Image releases before we go live.

We want to apply at least 3 PUM releases before go live.

The DEV instance will be at a lower PI level if we apply new PI to upgraded copy of PROD after each pass. There will be instances at different levels like DEV on 9.2.20, TEST on 21 and SIT on 22 per say.

This means the retrofits cannot be migrated directly from DEV to TEST. Retrofit needs to be done after each pass and until we freeze on the PI level it continues.