I wanted to use a vlookup formula to locate values using "data" as my
reference point and add them. There are several cells that reference "data,"
however, when I run my formula, can only pick one of the values up and not
add all the other values using "data."

=+IF(VLOOKUP(E18,'DD1921 Summary'!$C$18:$N$262,7,0),SUM(VLOOKUP(E18,'DD1921
Summary'!$C$18:$N$262,7,0),""))

This is the generic formula that locates one of the "data" values, but not
the sum of all the values using "data" as a reference point.