Most users do not bother with getting data on internal cell storage products, for the reasons that you describe.

The IWA reports should 'document' procedures, but these read as stored substrate in ASM3 cannot be measured separately and therefore is inferred though model calibration. ASM2 implies, but does not categorically state, that PHB storage can be assessed by respirometric techniques. For practical purposes I think you can take this, too, as being inferred through the calibration exercise. ASM2 does state that you can ignore PHB in the wastewater, so it is just being created by the MLSS; and then it becomes a parameter to adjust to match P-release data.

Look for Helen Haduc's PhD thesis; this will give you guidance on typical stoichiometric parameter sets.

People I work with are usually set up only for total & filtered COD; COD we estimate if possible using total & filtered BOD, but last job I did the BOD:COD ratio was not the usual 1:2 and we got better results by ignoring the BOD measurements; had we used them we had too much nondegradable COD and could not match the final effluent COD.