Google Sheets: filtering and matching a list treating NON-unique values

Question

I have a list (column A) of non-unique text values. Items from that list are put into column B (via dropdown data validation). Any items from column A that are missing in column B are shown in column C using this formula in C1:

=iferror(filter(A1:A, isna(match(A1:A, B1:B,0))))

Column A is technically sorted alphabetically, but it doesn't need to be, and I'm not sure that matters. Again, items occasionally repeat in column A. For every time a text value such as "x" appears in column A, but not in column B, column C has been showing every iteration of "x" in its list. But when "x" appears in column B just once, all iterations in column C vanish.

I'd like for the formula to treat every value in column A as unique, even when the strings are identical. If there are two iterations of "y" in column A, but only one "y" in column B, then C should have one remaining "y" left over.

I'm starting to think filter and match are the wrong functions to use for this.

Answer 1

See Test sheet

Main idea is to label data in column A and B with sequential number of occurrence for each position (e.g if item "Test" is repeated 3 times in column A - we need Test - 1, Test - 2, Test - 3). That's main reason why formula is so huge.

Once we get virtual data for both columns, i use similar logic with FILTER, ISNA and VLOOKUP to trace non-matching values.