Hi,
Are you suer that there is CE 7.31 system product. I know NW 7.31 is there but not CE7.31.
I could find that you have LM-MODEL-CE 7.30 which is the predecessor of LM-MODEL-CE 7.20 but has not got any system product defined to it.
ES FRAMEWORK 7.31 and BPEM ADOBE FLEX UIS 7.31 are also release but have not been assigned to any product.
I would suggest to check the below statement.
Upgrade from SAP NetWeaver Composition Environment 7.2
Make sure that you select "CE Product Description" when you maintain your system landscape data in SAP Solution Manager. This is a prerequisite for the Maintenance Optimizer to properly calculate the software packages for the target release.
1609441 - Add. info about the upgrade to SAP NetWeaver 7.3 EHP1
So there is upgrade patch to NW 7.31 but why you are not getting these component in the stack might be because above mentioned 7.31 are not assigned to product .
Thanks
Rishi abrol