As per 36.331 systemInfoValueTag is defined as below.
Common for all SIBs other than MIB, SIB1, SIB10, SIB11 and SIB12. Change of MIB and SIB1 is detected by
acquisition of the corresponding message.
If there is any change in MIB, SIB1 SIB10, SIB11 and SIB12 then systemInfoValueTag will not change. If we modify SIB2 to SIB9 then systemInfoValueTag value will be changed.
Suppose paging is happening for change in SIB1 then UE will read the updated SIB1. In this case systemInfoValueTag value will not change so UE will not read any other SIB.
Suppose paging is happening for change in SIB2 to SIB9 then eNodeB needs to changed the systemInfoValueTag value in SIB1, when UE will read the SIB1 then UE will find the change systemInfoValueTag value so UE will read the all relevant SIBs.