You can only have 12 channels of XDV70 with their original firmware (RF1) running on stage at once. If you upgrade the firmware to work with RF2 mode, you can get 14. But no more than that.
There's nothing to stop you using 12 V70s and 12 other UHF mics at the same time though. But if you want 24 identical systems, you'll need to look elsewhere. And pay a fair chunk out in licencing costs.
I don't know if this'll help, Dave...
But I've had great success in using extra transmitters to successfully run more pre-wired performers than you'd expect my eight XD-V70 receivers to handle.
Doing this requires a disciplined routine and would also require rehearsal for console "snapshotting" of individual level, dynamics and eq ...in the event that these parameters are vastly different between given individual contributors sharing a single receiver/mixer signal path.
With similar performers, it's an absolute "walk in the park."
Taking one such path as an example, performer "A" is currently onstage, knocking 'em dead, via a TBP12.
Meanwhile, my assistant is backstage, dressing performer "B" with a second TBP12, switched on and tuned to the same nominal "channel".
This second performer can neither be "PFL'd", nor appears at the console, as that XD-V70 receiver is "owned" by performer "A's" active transmission, right up until my assistant is able to switch off the "A" beltpack.
Within a second of the "A" switch-off, the "B" beltpack has initiated a fresh "handshake" and established its "ownership" of the XD-V70 receiver in question, wherupon the "B" signal is fully addressable from the console.
Although I've had no problems in doing this, I'm assuming that's because of the offstage rejection afforded by my P180 paddles, all the while maintaining excellent coverage of the performance area.
Otherwise, (at the very least) I'd expect reduction in viable range if such "sharing" was attempted.