It sounds to me like they have an incomplete set of records and that can only strengthen your case at the tribunal. But this is not our area of expertise so we asked our friends at the Tenants Union who sent us this response:
“As a general rule, if a landlord wants to rely on a rent ledger as evidence of a claim for arrears, the tenant should be given the opportunity to consider it. On the other hand, if the landlord does not have access to this evidence in the first place, then it will be difficult for them to establish the truth of their claim…
“Assuming this question relates to renting in New South Wales, have a look at section 37 of our Residential Tenancies Act 2010.”
37 Rent records(1) A landlord or landlord’s agent must keep a record of rent received under a residential tenancy agreement (a rent record).(2) A rent record may be kept in any form, and must contain any particulars, prescribed by the regulations for the purposes of this section.(3) A landlord or landlord’s agent must, within 7 days of a written request by the tenant, provide a written statement setting out the particulars of the rent record for a specified period.
(4) This section does not require a landlord or landlord’s agent to provide a written statement for a period to a person if the landlord or agent has previously provided a written statement for the same period to the person.(5) Subsections (3) and (4) are terms of every residential tenancy agreement.
Section 165 will also be of interest.
165 Notice to tenants of claims against tenants(1) A landlord, landlord’s agent or a person on behalf of a landlord who makes a claim for payment of a rental bond without the consent of the tenant must give the tenant:
(a) a copy of a completed condition report about the residential premises at the end of the residential tenancy agreement, and
(b) copies of any estimates, quotes, invoices or receipts for work for which the rental bond is claimed.(2) The documents must be provided within 7 days of the claim being made.(3) The documents must also be provided to the Secretary of the Department of Family and Community Services if the whole or part of the rental bond was paid by or on behalf of that Department.(4) A person who, without reasonable excuse, contravenes this section is guilty of an offence.Maximum penalty: 20 penalty units ($2200).