Dropdown List Created From 2 Columns Of Info?

I have a list of names in column B, I can easily put this into a list

I also have a different list of names in Column C

These two list are feeding from sharepoint and are updated regularly

What I want to do is create a drop down list that will list all the names in Column B and Column C, while keeping the initial lists in there separate columns

I have been trying to find a formula to lookup both columns and return all the names into another column (E) using the formula below

=IFERROR(INDEX($B$2:$C$600,MOD(ROWS(E$2:E2)-1,ROWS($B$2:$C$600))+1,INT((ROWS(E$2:E2)-1)/ROWS($B$2:$C$600))+1),"")

the plan been to just put column E into my drop down list, but this formula is returning alot of blanks between Column B + C in the list (there might be 100 names in column B and only 30 in column C)

To try remove the blanks I tried another formula pulling the info into Column F,

=IFERROR(INDEX($E$2:$E$5000,AGGREGATE(15,6,(ROW($E$2:$E$5000)-ROW($E$2)+1)/($E$2:$E$5000<>""),ROWS(F$2:F2))),"")

But while this did remove the blanks (about 500 blanks) it left me with about 70 "0" errors.