Need advice on how to catch up on state pension entitlements after being abroad for 10+ years

I stand corrected.
If the current rules ( that you have a choice of averaging or TCA) are the same in 2043 when the OPs and his wife retire, they can each pick and choose which approach gives them the best pension, but none of us can predict this. I doubt if it will be the same.

As part of the changes which were due to be implemented in 2021 (now deferred?), the proposal was to change the State Pension calculation model to the Total Contribution Approach only ie the 1/40th model. If I was a betting person I would wager that such a change will happen sooner rather than later. The Total and Average model is not the most equitable as its possible for someone with only 10 years PRSI contributions to get a full State Pension.