Another possibility is that, in his old age (perhaps due perhaps to previous Twilight experiences), the magus was getting a bit strange. Every time he visited the valley he would commission a new building, or a new wing to the manor house, or a tower. Only to change the focus on the next visit.
So now the covenant has a scattering of buildings, some nearly finished, some half completed, others having fallen in disrepair because there weren't enough covenfolk to maintain them all.
So we get the decrepit part, the diversity of styles and buildings, all within range of a single Aegis.