Relief for Contributions on Retirement

I retired from my PAYE job in March 2019, and haven't yet matured my Zurich Life pension plan. I have a decent sum of cash on deposit, though its % return is obviously minimal these days.
I look after my own tax affairs, and have used ROS for several years now. Normally I'd look at paying into my pension fund when making the October 31 return, thus reducing my tax bill, but for varying reasons I've had to skip payments occasionally. I've recently heard that as I've now retired from employment, I may be allowed to make another payment to the fund, and could allocate this payment against any of the past 4 tax years, rather than just the preceding year as is usually the case.
Can anyone confirm this ?
The other aspect I'd like clarification on - can deposit interest be included in the calculation on which pensionable earnings are totalled, or is that figure to be based on paid employment earnings only ?

The spread back is now only into the preceding year.
Deposit interest is deemed as “unearned income” and thus is not pensionable.

Thanks Conan for conirming re 'unearned income' being not pensionable.
I spoke with Revenue this morning and a very helpful lady there advised that I could go back 4 years or 'spread back' as you put it. Is there any documentation on this matter, as I can't find anything on Revenue's own website about it ?

ManWithDog said:

I spoke with Revenue this morning and a very helpful lady there advised that I could go back 4 years or 'spread back' as you put it. Is there any documentation on this matter, as I can't find anything on Revenue's own website about it ?

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I think the Revenue Pensions Manual might cover this as "relief for special contributions". See Para. 3.4 - https://www.revenue.ie/en/tax-professionals/tdm/pensions/chapter-03.pdf

"A claim for tax relief must be made within four years of the end of the year of assessment in which a contribution is made or is treated as having been made."