I have had a look at the configuration options and it appears there's none for the New Albums to be based on either creation date or modification date, or how many to list and for how long to keep them. I am presuming it's defaulting to modification date, and 25, from looking at its results - a lot of modifications were done recently to my library so some of my new ones have dropped off the list.
Would it be possible to have these options - modification/creation date, number of items to list, and for how long to keep them in it?