The booking window on your site is not a self-serve setting in the HomeRunner dashboard.
Why this happens. The calendar widget in the dashboard has a Booking Window field, but it only controls how far the embedded calendar widget displays. It does not change how much availability and pricing data your site holds.
How to extend it. To extend the window beyond 12 months, contact HomeRunner support. Tell them the number of days you want (for example 455 or 730; the maximum is 730) and which brands or sites the change applies to. Support raises the sync horizon on your connection and re-syncs, and your site picks up the extra months within minutes.
If you run several brands as separate connections, name each one in your request, because the change is made per connection.