Burden of proof when claiming priority

If, during the application or opposition proceedings, the applicant or patent proprietor introduced some differences regarding the definition of a certain chemical compound in a claim with respect to the definition in the priority application, and, despite these differences, asserts that the priority is validly claimed, the applicant or patent proprietor bears the burden of proof for this assertion (EPO Board of Appeal 21/11/2022, T 1303/18, UCB PHARMA / ROTIGOTINE POLYMORPH).