(8) No increase pursuant to paragraph (2) of this subdivision shall be granted by the DHCR, unless an application is filed no later than two years after the completion of the installation or improvement unless the applicant can demonstrate that the application could not be made within two years due to delay, beyond the applicant's control, in obtaining required governmental approvals for which the applicant has applied within such two-year period. No increase pursuant to paragraph (2) of this subdivision shall be granted within the useful life of an improvement or installation for which an increase was previously granted except with prior DHCR approval for required improvements. In addition, an increase pursuant to paragraph (2) of this subdivision shall not be collectible from a tenant to whom there has been issued a currently valid senior citizen rent increase exemption pursuant to section 26-509 of the Administrative Code of the City of New York, to the extent such increase causes the legal regulated rent of the housing accommodation to exceed one third of the aggregate disposable income of all members of the household residing in the housing accommodation. The collection of any increase in the legal regulated rent for any housing accommodation pursuant to paragraph (2) of this subdivision shall not exceed six percent in any year from the effective date of the order granting the increase over the rent set forth in the schedule of gross rents with collectibility of any dollar excess above set sum to be spread forward in similar increments and added to the legal regulated rent as established or set in future years. In no event shall more than one six-percent increase in the legal regulated rent pursuant to paragraph (2) of this subdivision be collected in the same