Combined Item number and serial number to be unique value

I have a report that sends out a DB mail alert when duplicate serial numbers are detected across company databases, and it works fine 99 present of the time, however we have had a couple of situations where it detects a duplicate serial number condition, but in those cases they weren't actually duplicates as they had the same serial number but different Item numbers. My code is looking at strictly serial numbers but apparently that is not 100 Percent accurate, so what I would like to do is ignore the results if the serial number is the same but the Item number is different.

This is the view (SSG_AD_AllSerials) that is called by the view that generates the report

SELECT        SERLNMBR, ITEMNMBR, LOCNCODE, DEX_ROW_ID, 'AMCHR' AS Company
FROM            dbo.IV00200
WHERE        SERLNMBR <> 'NONE'
UNION ALL
SELECT        SERLNMBR, ITEMNMBR, LOCNCODE, DEX_ROW_ID, 'ATI' AS Company
FROM            ATI.dbo.IV00200
WHERE        SERLNMBR <> 'NONE'
UNION ALL
SELECT        SERLNMBR, ITEMNMBR, LOCNCODE, DEX_ROW_ID, 'ATIMF' AS Company
FROM            ATIMF.dbo.IV00200
WHERE        SERLNMBR <> 'NONE'

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View that generates the report

SELECT        TOP (100) PERCENT SERLNMBR AS Serial_No, ITEMNMBR AS Item_No, LOCNCODE AS Site, Company
FROM            dbo.SSG_AD_AllSerials
WHERE        (SERLNMBR IN
                             (SELECT        SERLNMBR
                               FROM            dbo.SSG_AD_AllSerials AS SSG_AD_AllSerials_1
                               GROUP BY SERLNMBR
                               HAVING         (COUNT(*) <> 1))) 
ORDER BY Serial_No

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