The references to X501 and X690 have differenct format where X609 refer to both ITU-T and ISO/IEC while X501 only refer to ITU-T. Ignore this part if that is intentional.
The X690 reference seems incorrect. Seems like it refers to the 2015 version of ITU-T and the 2002 version of ISO
"ISO/IEC 8825-1:2002, November 2015."
https://www.itu.int/rec/T-REC-X.690-202102-I/en https://www.itu.int/rec/T-REC-X.501-201910-I/en https://webstore.iec.ch/publication/68163
The references to X501 and X690 have differenct format where X609 refer to both ITU-T and ISO/IEC while X501 only refer to ITU-T. Ignore this part if that is intentional.
The X690 reference seems incorrect. Seems like it refers to the 2015 version of ITU-T and the 2002 version of ISO "ISO/IEC 8825-1:2002, November 2015."