You can also try
=SUM(IF(FREQUENCY(IF(A2:A11<>"",MATCH(A2:A11,A2:A1 1,0)),ROW(A2:A11)-ROW(A2)+1),1))
(adapt ranges as necessary-unchecked-Commit as array formula with Ctrl+Shift+Enter)
which should count the number of distinct vendors in one go

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