What identifier rules do I need to adhere to when using AddSubType?

Question

I've defined the following inheritance hierarchy using protobuf-net and its RuntimeTypeModel

var model = RuntimeTypeModel.Create();

model.Add(typeof(LineFields), false)
    .Add(1, nameof(LineFields.Length))
    .UseConstructor = false;

model.Add(typeof(ArcFields), false)
    .Add(1, nameof(ArcFields.Length))
    .Add(2, nameof(ArcFields.Curvature))
    .UseConstructor = false;

model.Add(typeof(GeometryFields), false)
    .AddSubType(1, typeof(LineFields))
    .AddSubType(2, typeof(ArcFields));

My tests appear to pass but I'm somewhat uneasy about the identifiers used for the above AddSubType identifiers. Should these identifiers be different from any identifiers used in the sub-types?, i.e. should I rather be doing:

model.Add(typeof(GeometryFields), false)
    .AddSubType(101, typeof(LineFields))
    .AddSubType(102, typeof(ArcFields));

(is the AddSubType effectively doing the same as the ProtoInclude attribute as described here?)