If we disallow late injection in general, both injection and
reinjection, then we don't need Injection-Date.
Yes, but that's not realistic.
It should be a warning sign for a train of logic if the thing that one
declares not realistic is how all of Netnews currently works and what RFC
1036 requires.
It's realistic; Netnews has worked that way for decades. The question is
rather whether the benefits from changing it are worth the costs, and
proceduraly, whether it's worth reopening the topic rather than working
with what we've got now in USEFOR.
Users can poll their server, and then go offline for some time creating
articles with different days, waiting in their outbound for better
times. Then they go online again and try to post their articles.
That's one scenario where Injection-Date could be better than Date.
Or said off-line posting agent can rewrite Date when the message is
actually injected. That's what they have to do now. You lose information
for humans, but the protocol works.