So, I have something working… in the apparent absence of any sort of clear documentation that I could find. I had some time on my hands this afternoon, so had another look.

In T1621#149541, @werner wrote:

GnuPG stable (i.e. 2.3.2) has full support for several readers and tokens. This won't be backported to the LTS versions (2.2), though. Better switch.

I've recently acquired two Yubikeys: one Yubikey 5 NFC from my workplace, and shortly after, I bought a Yubikey 5C for my own personal keys… both security tokens have _different_ keys on them. (There are some questions being asked regarding the use of the same GnuPG key duplicated on separate smartcards; this is a different case).