I feel like this entire thread has been an elaborate attempt to demonstrate that you know an ISO definition. With the carefully constructed adjectives used to describe the definition ("standard technical meaning", "In a technical context") leading inexorably to the "ISO" gotcha.

To save others time, here's the ISO-8601 document which is apparently being referenced: https://dgn.isolutions.iso.org/obp/ui#iso:std:iso:8601:-1:ed...

"decade" is defined in 3.1.2.22:

decade time scale unit (3.1.1.7) of 10 calendar years (3.1.2.21), beginning with a year whose year number is divisible without remainder by ten Note 1 to entry: Decade is also used to refer to an arbitrary duration (3.1.1.8) of 10 years, however decade is not used as such in this document.