They don't want people using codes in the suffix field for a couple reasons. One is that it gives a false impression that that's a real thing that someone actually used with their name, which is what the suffix field is for. Another is that it sort of presumes that everyone agrees on the code system. Finally, code systems that are based on counting generations are quite susceptible to errors, especially in the sort of situation you're talking about. It might help keep track of people, but if you're keeping track of a skipped generation or doubled generation, it's just reinforcing a mistake. It's certainly encouraged to put that kind of info in the profile though, and if it's too late in the evening to keep track of it, it's probably best to edit it some other time. ;)