It's been many years ago; but if memory serves...the error code was part of a header in a server response packet. Expanding that header to include another field

It's been many years ago; but if memory serves...the error code was part of a header in a server response packet. Expanding that header to include another field would break all the clients and handler software. Eventually, a major release fixed the problem with a different header with expanded fields; but that was not a simple fix. Like I said, backwards compatibility CAN be the bane of innovation.