The following formula is used to show the value of the last figure that was
entered into any one row in my spreadsheet, looking at every 4th cell from
G12 to AN12.

=IF(COUNT(G12,J12,M12,P12,S12,V12,Y12,AB12,AE12,AH 12,AK12,AN12)=0,"",INDIRECT(CONCATENATE("R",ROW(), "C",((COUNT(G12,J12,M12,P12,S12,V12,Y12,AB12,AE12, AH12,AK12,AN12))*3)+4),FALSE))

I would like to use a similar formula, which would find the last figure
entered in any one row, but rather than showing the value of that cell, I
would like to show the value of the column header. For example, if the last
figure entered was in cell V12, I would like the result to show the value of
cell V1, the header for column V, i.e. Visit 6, so I know what the last visit
number was.

Any ideas?