A simple retentive question … but don’t know conventions based answer.
I suppose it’s divided based on whether law could be involved some where down the line, or the argument gets hottest eg “The Great Prentender” story.
Is it year hybridized, or year germinated (mine always from that year for environmental reasons - winter), or legally significant years such as patent year, or commercial intro year if “going to that end”?
It appears that’s up to you. Some report it as when the cross was made. Some, when the seedling first flowered. Perhaps it may be when it’s first marketed? I’m not aware of any “official” or “legal” requirement.
My impression has been that it is sometimes as late as one can get away with, for the simple reason that the date claimed sets the patent timer ticking.
Consider the number of crosses registered as being bred “before 20xx."
I don’t know this for a fact though.