https://www.business-standard.com/india-news/pm-modi-releases-commemorative-postage-stamps-book-dedicated-to-ram-mandir-124011800256_1.html
The stamp book is an attempt to showcase the international appeal of Lord Ram, and the 48-page book covers stamps issued by more than 20 countries
commemorative postage stampspm modireleasesbookdedicated
https://www.answers.com/collecting-hobbies/Are_commemorative_stamps_valid_postage
Certainly, that is what they were created for, to serve as postage. Just make sure the total face value of the stamps equals the appropriate rate for the...
commemorative stampsvalidpostageanswers