Collection creation from software metering

I am trying to create a collection based off of software not used in 180 days for firefox. (trying to clean up older version since it only updates when used). i created an report the looks to be working nicely but it differs from the results i get for the collection i create. the problem is that some users do a run as on firefox or it was launch by someone after they built the system. so software metering picks up that user that doesnt use the machine or the run as user, but in reality it has been run more recently by the actual user. does anyone have any thought or solutions. this is the query i am using:

select SMS_R_SYSTEM.ResourceID,SMS_R_SYSTEM.ResourceType,SMS_R_SYSTEM.Name,SMS_R_SYSTEM.SMSUniqueIdentifier,SMS_R_SYSTEM.ResourceDomainORWorkgroup,SMS_R_SYSTEM.Client from SMS_R_SYSTEM inner join SMS_MonthlyUsageSummary on SMS_R_SYSTEM.ResourceID = SMS_MonthlyUsageSummary.ResourceID INNER JOIN SMS_MeteredFiles ON SMS_MonthlyUsageSummary.FileID = SMS_MeteredFile.MeteredFileID WHERE DateDiff(day, SMS_MonthlyUsageSummary.LastUsage, GetDate()) > 100 AND SMS_MeteredFiles.RuleID = 16777418

for my report i found adding a

having datediff(dd,max(mus.lastusage),getdate()) >@numdays

this looks at just last usage of the exe for that specific machine it seem.