Hey Lawrence,
So, I'm not sure I got your point across, but I see you are trying to generate a favorite that would lead one to that page, there is really no need to check the WindowID, since it is irrelavant to the navigation. By adding through the menu option inside the portal, it will determine the ShortURL to that page and embed it in the URL. You can see the WindowID is there, but if you remove the WindowID, nothing will change, as it will lead to the navigation you were expecting anyway. You must set the portal to use ShortURLs then it will automatically generate a ShortURL to every navigation nodes you have in portal. You could then check the ShortURL leading to your custom page and attach it to the URL in favorites. Please, refer to this link to get more info on ShortURLs.
Please, forget the WindowID thing, it is surely not relevant for storing favorites 
I hope this helped!
Regards,
Gabriel.