How to model protobuf proto file

My application has various clients (say for example Client1, Client 2, Client3 ....and so on). Clients share some generic properties and has some unique data.

In my .proto file I want to model this kind of behavior. I came up with :

message MyClientsData {
    BaseClientData baseData;
    Client1SpecificData client1;
    Client2SpecificData client2;
... and so forth...
}

BaseClientData is the common data across all clients.

This works for simple use case when number of clients are very limited, but becomes hard to read if it grows. Is there some good practice on how to handle this kind of situation when there are unique data across different deserialization request?