I saw that prop in the movie. Never did see the date on it, but goddamn! Talk about it being set that far into the then-future.
That said, like you said, it might not line up with the sequels, so let's put that to one side for now, and if anything in the sequels doesn't contradict, we'll go with the prop.
Also, if anyone can find a copy of the 2003 promo comic for 28 Days Later (assuming it does exist), feel free to share it here so I can add to the timeline.
Updated the timeline with the first two stories (Development and Outbreak) from 28 Days Later: The Aftermath. Thankfully, those were easy to place in the timeline due to the mention of time periods between events.