Unable to copy Natural language formula down the column

This is what I see in H18...

= IF(ISERR(SEARCH("/",G$9:G$65536)),G18,LEFT(G$9:G$65536,(SEARCH("/",G$9:G$65536)-1)))& IF(F$9:F$65536=".", "","_" & F$9:F$65536 )& IF(E$9:E$65536=".", "","_" & E$9:E$65536) & IF(D$9:D$65536 =".", "", "_" & D$9:D$65536 )&IF(B$9:B$65536=".", "", "_" & B$9:B$65536) & IF(C$9:C$65536=".","", "_" & IF(ISERR(SEARCH("/",C$9:C$65536)),C18,LEFT(C$9:C$65536,(SEARCH("/",C$9:C$65536)-1))) )

if you drag this formula back up, the #NAME errors disappear. However, do you really need to search dow to row 65,536? can't you change that to something more realistic?