Combining Subtotal, if, left right etc with filter

[akenb]

Hi,
I have a list of "Customers" in column A (A2-A270) in my first tab.
In columns B-G (listing "Item name" in B1-G1) I have listed a year slash a number: e.g. 2018/1000 (years ranging from 2017-2020.
What I want to do is to be able to form a table per customer in a secondtab depending on which customer is visible after filtering in my first tab.

Tab 1:
[TABLE="width: 500"]
<tbody>[TR]
[TD][/TD]
[TD]Item1
[/TD]
[TD]Item2
[/TD]
[TD]Item3
[/TD]
[/TR]
[TR]
[TD]Customer 1
[/TD]
[TD]2017/2000
[/TD]
[TD]2018/890
[/TD]
[TD][/TD]
[/TR]
[TR]
[TD]Customer 2
[/TD]
[TD][/TD]
[TD]2020/8950
[/TD]
[TD]2017/780
[/TD]
[/TR]
[TR]
[TD]Customer 3
[/TD]
[TD]2018/5000
[/TD]
[TD][/TD]
[TD][/TD]
[/TR]
</tbody>[/TABLE]


This table in tab2 I want to have like this:
Items on rows, years in columns and in the cells in between I want to list the number given in column B-G in my first tab.

Customer 1 chosen with filter in tab1 -->
Tab2:
[TABLE="width: 500"]
<tbody>[TR]
[TD][/TD]
[TD]2017
[/TD]
[TD]2018
[/TD]
[TD]2019
[/TD]
[TD]2020
[/TD]
[/TR]
[TR]
[TD]Item 1
[/TD]
[TD]2000
[/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]Item 2
[/TD]
[TD][/TD]
[TD]890
[/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]Item 3
[/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
</tbody>[/TABLE]


I have the following formula but it doesn't take the filtering in tab 1 into consideration. How can I do this?
=IF(VALUE(LEFT(Tab1!B2;4))=Tab2!B1;VALUE(RIGHT(Tab1!B2;(LEN(Tab1!B2)-5)));0)
if
Tab1!B2= statement for item 1 customer 1
Tab2!B1= year in table in Tab2

I know you can use the formula subtotal for filtered values - but how do I integrate if, left, right formulas etc.?
It is okay that the table in Tab2 only works when there is only one customer visible in filter i Tab1.

Thank you.