I would suggest that you clarify with the Pension Unit of the Department. I found the following in their General Information advice:
"How is payment for this purchase made? –Lump Sum or Periodic Deduction from salary - Purchase by Lump sum Teachers who choose to purchase notional service may do so by one lump sum at any time prior to retirement or by making one lump sum payment each year up to the year or retirement. Lump sum payment in year of retirement must be made at least six weeks before retirement date. The teacher has the option to choose how to make these payments and must indicate this choice in the Contract. A teacher who has an AVC or private pension scheme may opt to purchase notional service using the appropriate fund provided that this is clearly indicated in the application form. The fund may be transferred by electronic transfer at any time prior to retirement. A delay in fund transfer will delay payment of pension benefit and lump sum. Transfer of AVC fund is subject to stringent conditions and subject to receipt of completed Declaration form when signing Contract for Notional Service Purchase."
I'm not familiar with Public Service pensions so it might be a better query for the Public Service Pension forum. Do you have a separate pension fund either related to a previous / separate employment or do you have one in parallel with your Teachers position for Additional Voluntary Contributions (AVC)? I googled the following so I'm assuming that this applies to you?
"AVCs are "Additional Voluntary Contributions". They are extra savings that you build up, separate from your teachers' pension.
Here's how they work:
You make regular contributions to the plan. Contributions are eligible for tax relief, so you can reduce your tax bill. Your money is invested, and there will be good and bad years, but it is carefully managed. Your AVC is designed to grow towards your retirement. You can't access your AVC until you retire, and if the worst were to happen your AVC would go to your family.
When you reach retirement, it's time to access your AVC's. First, you'll top up your teachers' Lump Sum to the maximum allowable - this part is tax-free.
Next, you will use the balance to top up your taxable pension. The more you can save and grow the more affordable retirement will be. AVCs work best when you maximise tax relief on the way in and minimise tax owed on the way out.
AVCs are suited to those with short service or interested in retiring early."
Do you intend to make one lump sum payment in the year of retirement and is that coming out of a Teaching AVC or separate private pension?
If the lump sum is coming out of an AVC (private pension) then I think that you will need to initiate that process yourself a few months before your retirement date in order for the AVC (Private pension) to be matured and the 25% lump sum processed several weeks before your retirement date. You will then need to use that lump sum to pay for the Notional Service at least six weeks before retirement date as per above quote. The AVC (private pension) is a separate vehicle from your normal Teachers pension.
The question still remains as to whether that lump sum contribution 6 weeks before your retirement date can be claimed against the previous year. The above General Information note also states:
"Tax relief for periodic purchase contributions is given at source through Payroll. However, for purchase by lump-sum option, tax relief must be claimed directly from the Revenue Commissioners. Please note that tax relief limits cover all superannuation contributions paid (including contributions under the Spouses’ and Children’s Pension Scheme)."
That appears to me that you claim the tax relief yourself and its up to you which year you claim it against. If you claim it prior to 31st Oct then you can claim it against the previous tax year. You will need a Certificate or detailed receipt of the payment which I assume that you will receive from the Department?
Revenue detail below
"How to claim the tax relief
If you are a Pay As You Earn (PAYE) worker
Usually your employer deducts the contributions directly from your
pay, and will give you the tax relief due. If your employer does not deduct the contributions, you can claim the tax relief in myAccount by following these steps:
- Sign in to myAccount.
- Click 'Review your tax 2020-2023' under 'PAYE Services'.
- Request a Statement of Liability.
- Click on 'Complete Income Tax Return'.
- Go to the 'Tax Credits and Reliefs' page.
- Under the 'Your job' section, select 'Additional Voluntary Contributions (AVCs)' or 'Personal Retirement Savings Accounts (PRSAs)', and input all details regarding your policy.
- Complete and submit the form.
Sign in to myAccount
Note
To claim AVCs, a copy of the certificate, or detailed receipt, must be submitted when filing your Income Tax Return."
In conclusion, it looks like you can backdate the claim yourself subject to the 31st Oct and Cert/Receipt requirements but best to check with the Pension Unit and/or possibly your Union. Hope this helps.