Should a sage of heraldry choose to establish a location where they can be approached and matters of heraldry discussed, the character is likely to receive from 2-8 visitors a month and 3-30 letters asking for registration, adoption of new symbols or to determine the accuracy of potentially falsified documentation. There is a 5% chance that any one of these may be a royal request, and a 15% chance that they will be noble in origin. 90% of such investigation will be conducted through subordinates, but 1 in 10 royal or noble requests will be conducted in person.
Only 5% of requests or investigations will prove to be legitimate.
While a sage does possess the ability to falsify documents as an expert would, circumstances also provide the sage the potential for simply legitimizing the individual as a distant cousin or personage within the existing power structure of the chosen mega-culture. Since the sage's word is typically used as the standard for legitimacy, it is more sensible for the sage to establish legitimacy rather than falsify it.
Typically, legitimacy is granted by royalty or nobility based on communication with a sage, after all.
With regards to the detection of legitimacy, a sage will recognize false documentation or heraldic symbols in half the usual time. If encouraged, sages of heraldry will have conduits by which they will be able to communicate with families if an individual makes claims to a false lineage.
See Heraldry, Signs & Sigils