IF your %TRACK% for
1970_001a - Golden Earring - Back Home
currently contains
1970_001a
IF your %TRACK% for
1970_001b - Golden Earring - This Is The Time Of The Year
currently contains
1970_001b
If this is correct, you could just use
%TRACK% - %ARTIST% - %TITLE%
to build your new filename
If you have something else in your %TRACK%, please show us the real current content with a screenshot.