Need cell to show blank but number comes up due to adjacent formula

[Caveman1964]

Hi,
I have a formula in cell picking up running values. But when nothing is there, its giving me a number. I want it to show blank.
I assume because there is a formula in that adjacent cell.
this is what it shows. Where as E is the customer its picking up from column A, and F is the amount of times that customer shows up from A.
formula in F is referencing E and formula E is referencing another column.
Formula for E is {=IFERROR(INDEX($A$77:$A$3500, MATCH(0,COUNTIF($E$76:E90, $A$77:$A$3500), 0)),"")}
Formula for F is =IFERROR(IF(ISBLANK(E91),"",COUNTIFS(A91:A$375,E91)),"")
Column A is the running entries for customer, so it will have many duplicates.
e79 is blank except for formula in it.
[TABLE="width: 500"]
<tbody>[TR]
[TD="align: center"][/TD]
[TD="align: center"]E[/TD]
[TD="align: center"]F[/TD]
[/TR]
[TR]
[TD]77[/TD]
[TD]Customer 1[/TD]
[TD]4[/TD]
[/TR]
[TR]
[TD]78[/TD]
[TD]Customer 2[/TD]
[TD]5[/TD]
[/TR]
[TR]
[TD]79[/TD]
[TD][/TD]
[TD]273[/TD]
[/TR]
</tbody>[/TABLE]
[TABLE="width: 377"]
<tbody>[TR]
[TD]This is way out of my league, I'm already in over my head. I would appreciate any of you Gurus help. I don't even know how I got this far, weeks of reading internet and trying.
Background of formula.
New customers are entered on sheet 2 column L, sheet 3 picks up those and puts them in sheet 3 column A.
sheet 3 column E picks up customer and disregards duplicates and places name of customer. Column F shows how many times that customer shows up.
Looking at this, its not a good explanation. Hoping one you can see in my formula some way to make column[/TD]
[/TR]
</tbody>[/TABLE]

Thank You ahead of time for even reading this!

 

[Fluff]

For col F try
=IFERROR(IF(E91="","",COUNTIFS(A91:A$375,E91)),"")

 

[Caveman1964]

WHEW!!!! ....Oh my, yes it worked perfect! That just lifted a load off....I feel great joy right now! lol.....I am learning from all of you. I pick up a little at a time.
Thank You Thank You and Thank you..............stress relief. I got so frustrated last night, I threw in the towel. You are a blessing.
Wishing you a wonderful day!

 

[Fluff]

Glad to help & thanks for the feedback