Yes, you have it exactly.
In the case of any truly anonymous gifts (where even the organization doesn’t know who it came from), from a dollar left at the front to a large bequest, is USUALLY to associate it with an anonymous contact record. Make sure to give the contact record an activist code so you can easily remove it from lists when needed.
For those smaller gifts consolidating them into is usually fine. The case of a larger planned gift that might require ongoing management, or if a specific entity is managing multiple anonymous bequests, there may be case where you want it to have its own record. In that case create an organization called “Anonymous Planned Gift(s)- Managed by the Law Offices of BSweeney and Conley” or something similar. And, again use activist codes to make it easy to identify.