For Cisco 65XX Catalyst switch some module's serial number are not reflecting in SRM, though they are showing in Spectrum Entity View
SRM serial numbers are populated from NRM_LineCardData attribute.
Release : 10.4.x
Component : Spectrum Reporting
This device is is supporting proprietary CISCO-STACK-MIB.mib which also has the ENTITY_MIB.mib.
For collecting chassis information Spectrum gives priority to proprietary CISCO-STACK-MIB.mib and that's the reason ChassisMgr attribute is linked to CATStackApp model handle.
In this case NRM_LineCardData is derived from CISCO-STACK-MIB.mib (NOT from ENTITY_MIB) . This is functioning as designed.
There is an enhancement that uses ENTITY_MIB as first priority for populating the NRM_LineCardData and will be available in 21.2.4 .
The release 21.2.4 will be GA'ed tentatively in October 2021.