Column C is a column of number
Column E is a column of dates

I want to sum every number in C with no corresponding date in E. Seems
simple, but . . . .

=SUMIF(E:E,"" & DATEVALUE("1/1/1980"),C:C ) will sum everything with a
date, but I've been unable to figure out how to sum everything without a
date. Replacing the "" with "<" returns zero (0).