The raw numerics are a standard set used across the entire IRC network system. If these numbers were to change, then a lot of scripts that use those numerics might be good one day, but useless the next. It makes no sense for them to change, and quite frankly the numerics that I use in my scripts are still the same as when I started coding in mIRC nearly 5 years ago.
The standard set of raw numerics can be reviewed here
Some networks use non-standard numerics for certain items, but the standards still apply to all networks and IRCd's