Verify Data List

Can Anyone Help?
I Have A List Of 3000+ Company Names On A Ledger, And Some Of These Have Been Incorrectly Spelt, Entered Etc.

I Need To Be Able To Check To See If Which Company Names From List A1-a3000 Do Not Equal Any Of The Company Names From List B1-b250
Highlighting The Incorrect Item In Cells C1-c3000 With A "ok" Or "check Dat" Flag.

List B1-b250 Are The Correct Items
List A1-a3000 Have Been Entered But Many Are Incorrect.

Thanks.,

Enter the following formula in cell c1 and copy it down to cell c3000

if(isna(vlookup(A1,B$1:B$250,1,false)),"Check dat","OK")