(66)In order to improve legal certainty, the respective time limits within which an issuer is to publish a supplement to the prospectus and within which investors have a right to withdraw their acceptance of the offer following the publication of a supplement should be clarified. On the one hand, the obligation to supplement a prospectus should apply when the significant new factor, material mistake or material inaccuracy occurs before the closing of the offer period or the time when trading of such securities on a regulated market begins, whichever occurs later. On the other hand, the right to withdraw an acceptance should apply only where the prospectus relates to an offer of securities to the public and the significant new factor, material mistake or material inaccuracy arose or was noted before the closing of the offer period and the delivery of the securities. Hence, the right of withdrawal should be linked to the timing of the significant new factor, material mistake or material inaccuracy that gives rise to a supplement, and should apply provided that such triggering event has occurred while the offer is open and before the securities are delivered. The right of withdrawal granted to investors owing to a significant new factor, material mistake or material inaccuracy that arose or was noted during the validity period of a prospectus is not affected by the fact that the corresponding supplement is published after the validity period of that prospectus. In the particular case of an offer that continues under two successive base prospectuses, the fact that the issuer is in the process of having a succeeding base prospectus approved does not remove the obligation to supplement the previous base prospectus until the end of its validity and grant the associated rights of withdrawal. To improve legal certainty, the supplement to the prospectus should specify when the right of withdrawal ends. Financial intermediaries should inform investors of their rights and facilitate proceedings when investors exert their right to withdraw acceptances.