The electoral register is not updated until 15th February. Therefore anyone who registered to vote in the last year, or changed the address to which their polling card is sent, will not appear on the electoral register in the event of there being an election prior to 15th February. Members of the public should check with their local authority to ensure that they are put on the supplementary register, and would need to do this at least 15 days before the date of the election.
More information can be found here: https://www.thejournal.ie/general-election-2020-draft-register-problem-4964913-Jan2020/?utm_source=shortlink&utm_campaign=email_share