Jem is quite right.
But of course, I did say 8key flutes right at the start of the post, to avoid confusion.
It's helpful to know RR kept separate serial number series for the various flutes, and 8key simples were the first, of course.
though there are variants of Bb flutes and the occasional F flute (I've only catalogued a single F flute in the series), and the rare key or even 7key (like a boxwood one i own), the sequence of simple system flutes is pretty straightforward.
But the boehm systems, carte systems, etc, all have their own sequence, even the piccolos have their own.
useful to know, of course.
i should note that Pratten flutes (Hudson began it, then Boosey continued it) were the first in which all the parts had a serial number to match.
I believe the idea of serial numbers was first borne, if i recall correctly, by Monzani.
Rudall, of course, only placed the serial number at the heart piece of the main maker's mark, just above the C# hole.