Are Papal Encyclicals in Effect Unless Revoked (e.g., Acerbo Nimis)?

In the 1905 papal encyclical (Acerbo Nimis) of Pope St. Pius X, one finds, for example: > 19. I. On every Sunday and holy day, with no exception, throughout the year, all parish priests and in general all those having the care of souls, shall instruct the boys and girls, for the space of an hour from the text of the Catechism on those things they must believe and do in order to attain salvation. - [*Acerbo Nimis*](https://www.vatican.va/content/pius-x/en/encyclicals/documents/hf_p-x_enc_15041905_acerbo-nimis.html) QUESTION: Has *Acerbo Nimis* been revoked; or is it (as it would seem) largely being ignored? In general, are papal encyclicals always in effect unless otherwise specified or revoked? Thank you.