>> Can people give me some advice/experiences on getting my serial
>> number back down to this value i.e. YYYYMMDDNN
Read RFC1982: Serial Number Arithmetic.
And next time you post something to the newsgroup, kindly supply a
real email address. The newsgroup is bidirectionally gatewayed into a
mailing list, bind-users at isc.org. Nonsense email addresses are
anti-social.