V5.25 of Compress For IMS included the following instructions:
Next run INSTALL9. This job assembles and link-edits the source contained in SHRINK.IMS.SOURCE to create the program modules. The program modules use the IMS/VS macros: DFSLEV, ISCD, IDLI, IMODULE, and ISWITCH. To ensure valid macro expansions during the assemblies, use the IMS/VS macro library that relates to the IMS/VS release you are currently using. You must reassemble these modules whenever you change IMS/VS releases.
Now that Compress has been incorporated into Database Management Solutions r15.0, are there still any special requirements when we upgrade IMS levels?
There shouldn't be any special requirements. Since IMS Tools 15.0, Compress handles different versions of IMS in the same way as the rest of the tools - if there is an IMS version specific code, there is a 'suffixed' load/object module for each supported version of IMS (10,11,12) and the right one chosen at runtime based on the detected version of IMS.