Hi Perplexed,
I'm not sure why you think this is misleading, anyone who had obeyed the laws in place at the time would have paid 35% in Spain and been given a credit for it in Ireland.
The reclaim is obviously not for the entire 35%, it is only for the portion over the 15% that was being charged to Spanish locals at the time. This would merely entail declaring the reclaim on your next Irish tax return and paying an extra 5% to top up your Irish liability to the 20% payable here.
For the potential gain I'm not sure that I'd agree that it is a huge burden.
It's not yet certain that this will actually be refunded yet by the way, the Spaniards are fighting it as far as I'm aware.