A Certificate of Residence (COR) is proof that you are a tax resident in the country you claim residency in.
Your COR should explicitly mention all the years for which you are filing a Dividend Withholding Tax (DWT) reclaim application.
For example, if you are applying for a Swiss DWT refund for dividends received in 2023 and 2024, as a Spanish resident, you will need to obtain a Spanish COR that specifically mentions 2023 and 2024. Additionally, the COR must state the double tax treaty between the two countries — in this case, it should mention both Switzerland and Spain.