Why do QBFC interfaces (eg. ICustomerRet) only make some properties available?

I am experimenting with the QuickBooks Foundation Classes (QBFC) but find that only some of its interfaces' properties are available. For example: Type myType = typeof(ICustomerRet); foreach( PropertyInfo info in myType.GetProperties(BindingFlags.Public | BindingFlags.Instance | BindingFlags.GetProperty) ) { Console.WriteLine( "info.ToString() ); }

This prints: QBFC13Lib.IQBIDType ListID QBFC13Lib.IQBStringType EditSequence QBFC13Lib.IQBStringType CompanyName QBFC13Lib.IQBStringType AccountNumber

However the interface, itself, has many more properties: [[Guid("DF330518-953C-4813-BAEC-F65DDBBFEB5B")] [TypeLibType(4160)] public interface ICustomerRet : IQBBase { [DispId(47)] IQBStringType AccountNumber { get; } [DispId(36)] IQBBaseRefList AdditionalContactRefList { get; } [DispId(58)] IAdditionalNotesRetList AdditionalNotesRetList { get; } [DispId(35)] IQBStringType AltContact { get; } [DispId(30)] IQBStringType AltPhone { get; } ...

If I create my own version of the interface (eg. ICustomerRet2) as just a copy & paste of the original then running the code against ICustomerRet2 shows all of the properties.

What am I missing?