Remember the RC candidate only comes with the most basic stlyes and sounds by default and everything else needs to be added manually.
Ah, okay, thanks a lot, that was the crucial hint! Since namida had lifted the restriction of "official styles only" after the experimental phase, I assumed the styles folder shared with the RC was a complete one, just like with the official releases themselves.
That said, the L2 tilesets are part of the official tilesets, so right after orig and ohno, it was still not implausible to assume those would be part of a "minimal" styles download.
The reason I didn't notice whether or not the L2 styles are missing from the RC3 download is because...
Did you by any chance copy your "styles" folder, but not your "sounds" folder, from an existing installation?
Yes, I did indeed copy my styles folder over, mainly to have all my custom sprite sets in the new version. But even if I've overwritten an older version of the L2 Space tileset, that itself shouldn't be a problem, given that the sounds are stored elsewhere anyway.
So the actual issue was apparently just that I never thought of having to copy sounds over to the RC folder manually, too. The only custom sound I ever added myself is the one for the one-use leaf trap from my Autumn tileset, but I already sent that to Nessy a while ago, so it's part of the official styles download now. I just didn't realise that the official styles download for the RC is smaller than the official styles download for any given stable version.