INDEX(MATCH => Using IF Statement

[NEW_2VBA]

Hello!
The formula below populates the Billing Month from another Lookup table based on the Date Range.
It works, however I'm wondering, if there's a simpler way to rewrite this formula to include an IF statement. I need to reference a different Range for the INDEX, based on the the client Names in column F.

Current formula:
=INDEX('BillingSheet'!$J$3:$J$15,SUMPRODUCT((E2>='BillingSheet'!$K$3:$K$15)*(E2<='BillingSheet'!$L$3:$L$15)*MATCH(ROW('BillingSheet'!$J$3:$J$15),ROW('BillingSheet'!$J$3:$J$15))))

Need to add:
=IF(F2="CLIENT1",INDEX('BillingSheet'!$J$3:$J$15,SUMPRODUCT((E2>='BillingSheet'!$K$3:$K$15)*(E2<='BillingSheet'!$L$3:$L$15)*MATCH(ROW('BillingSheet'!$J$3:$J$15),ROW('BillingSheet'!$J$3:$J$15)))),"I think here I would copy the formula using different Range IF F2 = CLIENT2 & CLIENT3")

 

[mikerickson]

Helper columns are your friend.
Put the first formula in X2 and then put the formula =IF(F2="Client1",X2, "not one client") in some other cell.

I know, there are huge monster formulas on this site often, but in practice, its much easier to create (and maintain) formulas that get the right result by using helper columns, than it is to decipher monsters.

 

[NEW_2VBA]

Thanks! I'll try that!

 

[NEW_2VBA]

This sort of works; --> the formula in X2 has specific cell reference so I'm unsure how to make it relative since I'm indirectly using it in an IF statement.
When I copied & pasted down it populated results based on date in E2 only.