Just noticed something else that deserved a mention.
On some of my puck mice, the back panel uses the 'blue' holographic, like the one on the original Bondi Blue iMac and tray-loading iMacs (behind the port door). But on other puck mice, the holographic is the 'graphite' one, whether the mouse itself is fruit-coloured or graphite.
I can't be sure, but I'm guessing that the puck mice adopted the graphite holographic back when the iMacs became slot-load. The graphite holo is the same as the one used on original Sawtooth G4 Power Macs (which was later removed with the Gigabit Ethernet models in 2000).
I've been confused by this aspect for a while, because it's obviously really easy to interchange the back panels of puck mice, so it's possible that some I own have already been swapped around in the past. Who knows.
View attachment 1945232
And, there are also some mice where the panel is upside-down:
View attachment 1945233
A probably good way to determine why one has graphite and the others have bondi is to provide the serials (or a pic of them) beneath the covers. I have a hunch that either the manufacturing code, date code, or both, on the graphite cover variant will depart from the ones which use the bondi variant — much like the keyboard counterparts posted earlier in this thread (the bondi label shows NK850, or end of 1998, and the other shows NK938, which is later 1999, after the fruit iMacs and Power Mac G4 were announced.