@Blue-Moon
In the attached file, the formula in Sheet2!B2 is:
=VLOOKUP(A2,
StorePercent,
2,0)
Note that StorePercent is defined as:
=Sheet1!$A$2:INDEX(Sheet1!$B:$B,COUNTA(Sheet1!$A:$A))
You can add stores and their corresponding percent in Sheet1 without any required modification in VLOOKUP in Sheet2!B2.
Please test it and inform me of your thoughts thereon.