SMSY system landscape data best practices

Dear SAP gurus,

Does anybody know where I can find System Landscape Data best practices/documentation for different SAP Solutions like SAP ERP, Solman, Portal, PI, etc?

I dont want to have info about how to set it up or achitecture etc... just information like:

- Can a technical system have more than one active product versions?For example SAP ERP 6.0, SAP EHP2 FOR NETEAVER 7.0, EHP5 FOR SAP ERP 6.0.

- What product instances should have SAP ERP6.0?

I need this information because Im struggling cleaning the data using LVSM and I get errors like:

"Some software components not covered by configured product instances"

"Product system <SID> has multiple active standalone product versions"

So I can make sure that all data in SMSY is correct which I am not sure...

Thanks in advance, Marc