Append a value at the end of the list, only if does not exist. in Excel

I do have 200 voluteers receiving a gift from a donation, All of them have volunteer cards What I want to achieve is a simple duplication control system A volunteer come in , we type or scan his Badge, The easiest thing is to check if the value exists So lets say IN Column A1 I add the number Column B1

  A      B
VAlue Result

and column A in Sheet 2 has all the numbers

So its easy with a function like this to check if the number exists

=IFERROR(IF(MATCH(A2,Sheet2!:$A$2:$A$1000,0),"Yes"),"No")

If the number does not exist I want to Append in Sheet 2 in column A

How I should do it