A couple of weeks ago I set readers the challenge which can be found here.
Once again, some truly excellent responses and a noticeably collaborative attempt towards obtaining our final, minimal-length solution. So many thanks to all who contributed: Alex, John Jairo, Lori, Snakehips and Will!
And that solution, at 108 characters, is:
=LOOKUP(,0/FREQUENCY(0,2^-(LEN(Q5:Q77)>4)/MMULT(SUMIF(U3:U28,MID(Q5:Q77,COLUMN(A1:G1),1),V3),1^V3:V9)),Q5:Q6)
How does it work?