CHY3 enduring certificate simply enables the charity to claim tax relief if you donate €250+ in any of the five years covered by the form. It simplifies the tax relief process for both you the donor and the charity. It’s the most effective method for charities to claim the tax rebate. Note it does NOT commit you to making donations to the charity.
CHY4 Annual Certificate only allows the charity to claim tax relief for the year in which you made the donation. If you donate to the charity in any following year, you will need to complete the CHY4 form again.