Remove Duplicates not working and M code for counting duplicates in a new column is required

Hello All,

I am trying to remove duplicates from Serial Number column but still few are left . Why remove dublicates are not working please find below the M code :-

#"Sorted Rows" = Table.Sort(#"Filtered Rows5",{{"Serial_Number", Order.Ascending}}),
#"Buffer Table" = Table.Buffer(#"Sorted Rows"),
#"Removed Duplicates" = Table.Distinct(#"Buffer Table", {"Serial_Number"}),

before this still i have to remove :

#"Filtered Rows5" = Table.SelectRows(#"Filtered Rows2", each [Serial_Number] <> "XXXX" and [Serial_Number] <> "DELETED" and [Serial_Number] <> "V0147" and [Serial_Number] <> "Delete" and [Serial_Number] <> "DUMMY" and [Serial_Number] <> "DUPLICATE" and [Serial_Number] <> "ERROR" and [Serial_Number] <> "FB0383" and [Serial_Number] <> "DUPLICIDADE" and [Serial_Number] <> "N/A" and [Serial_Number] <> "ABC" and [Serial_Number] <> "ABCD" and [Serial_Number] <> "xyz Regions" and [Serial_Number] <> "C" and [Serial_Number] <> "A" and [Serial_Number] <> "UNKNOWN" and [Serial_Number] <> "NA" and [Serial_Number] <> "N A" and [Serial_Number] <> "X4FL62J87395"),

Why power Query is passing these through ?What to do and in order to find these i worte a DAX code to check if still Duplicates are avaialble -