Upon opening Sibelius or starting new score, you’re generally presented with the Quick Start interface. One of the tabs in that interface is the Recent tab, from which you can select scores you’ve worked on today, this week, this month, or further back than that.
In time, Sibelius can get confused and either display scores that you haven’t worked on in a while, or omit scores that should rightfully appear.
The same problem can happen in File > Recent, where a list of recent documents and recent places appear.
Fortunately, this is where you can correct the problem by clicking the Clear Recent Documents button at the bottom of the screen. You’ll lose the history of any documents and places currently in the list, but if they were inaccurate already, then it’s probably better to start over anyway.
Quit Sibelius and re-launch it for this to fully take effect in the Quick Start dialog as well as in the File > Recent list.