Under SEPA legislation, setting up a DD requires a signed mandate. There is a dispensation in Irish legislation for Irish originators taking a mandate on Irish bank accounts, to support the DDplus scheme which pre-exists SEPA. They don't require a signed mandate.
If you want to use a non-Irish bank account, you need to fill in a paper mandate, and the DD originator needs to keep this on file. Some originators are by passing this and taking details online / over phone. They are in breach of terms and conditions with their sponsoring bank, and SEPA scheme rules so leaving themselves open to claims.
The current account switcher process is completely flawed in how it operates. I'd estimate considerably less than 10% of those who move their primary account actually use the process.