Change this:

AND A.[ACCT] NOT IN
            (
              SELECT
                [ACCT]
              FROM
                [dbo].[TABLEB]
              WHERE
                [FSCD] IN (
                            'BIQ'
                            , 'BCU'

Question, can an Account (Acct) have multiple FSCD's and that the following subquery is to exclude all accounts that has an FSCD of 'BIQ' or 'BCU' even if there is...

Without more information, hard to say.  Since it looks like you can't provide much it may not be worthwhile to ask to see the execution plan or the definitions of...

Not sure what you are asking, could be that it is late on Friday and I am looking forward to the weekend.

Just going to ignore my question?

Having helped my daughter with learning Python for one of her CS classes this question was easy.

Please explain the business case for trying to reuse the gaps created by deleting data.  You are far from running out of identity values so, as someone else said, it...