Hi I want to check if a value is present across multiple worksheets

So I have a list of integers in the cover sheet
1
2
3
4
5

I then want to look to see if "1" is in column A of worksheet"Main", if it is then display "MAIN" if it is not then check column A of worksheet"Lower", if it is there display "LOWER" if it is nowhere then display "NONE" I had the following formula which works fine except for showing N/A instead of "NONE"

=IF(VLOOKUP(A1,Main!$A$1:$A$5,1,TRUE)=A1,"MAIN",(I F(VLOOKUP(A1,Lower!$A$1:$A$5,1,FALSE)=A1,"LOWER"," NONE")))

however if I replace the numbers above for a string such as names it is very sporadic as to whether it works or not, some will return the correct value and others will return the wrong value, i.e. it is present in one of the worksheets yet still returns an N/A value

Any thoughts as to why it works with an integer but not a string?

Thanks

Richard