extract number values from a table and make a list

To keep absolute reference to one column /row when using tables you have to use INDIRECT:
B2:
=INDEX(Table1,MATCH($A3,INDIRECT("Table1[Client]"),0),MATCH(B$2,Data!$A$1:$L$1,0))

or
=INDEX(Table1,MATCH($A3,INDIRECT("Table1[Client]"),0),MATCH(B$2,INDIRECT("Table1[#Headers]")))
Drag that accross