It would apply if your 2000 Retro was as "twisty" as the newer Retro models.
If the recommended mast is written on your 9.5 m2 2000 Retro, I'd follow that
I have not been able to find the rigging spec's for the 2000 Retro, so I'm unsure if it took a 490 or a 520 as the "best mast".
You 2000 Retro had a much tighter leech than later versions, so if it's working well on the 490 cm mast, with good handling and an appropriate amount of twist, might be better to continue sailing it that way.
I think we decided earlier that the recommended mast was a 490 cm, didn't we?
The amount of twist, and the stiffer IMCS 32-34 520 masts have affected the design of
the later Retro sails.