The rules (or suggestions) for using contacts don't apply directly for BR. Like many D&D conventions, they assume a rootless party wandering along and poor in coin, seeking a friendly face to help them along.

Birthright characters are often extreamly wealthy (so could easily afford all of the minor freebies contacts might offer), and in many respects, its the PC's who make for the ideal "contacts", not the contacts themselves. If the PC runs an affiliation, domain, holding, or realm, who exactly wants to get to know whom?

Any closed social system tends to have a strong element of "its not x, its who you know." Contacts are tremendously important, but not the kinds of contacts presented. Most BR characters don't need a contact who will cast Identify for free once per week for them. They either have a court wizard who they can access, their organization is allied to a source wizard, or they can pay the fee without noticing the expence.

Birthright contacts often are people who know what's going on in another organization who can bring you up to date when you meet them, or will send you word of things you are interested in. Contacts are something less that full time informers. They are informal, they are people you know. Full time informers are members of your organization. Good contacts to have are people who watch your enemies and potential enemies, and people who can help you talk to friendly factions in unfriendly or indifferent courts.