eBay and Craigslist finds

Yes, these were separate.
Campagnolo was integrated with the holders.

And yes, these parts guide the wheels / enable a quicker wheel change.
Without these guides, the tyre may bump onto one of the brake pads.
These guides help the wheel go quickly between the pads.

Guides are saparate (as on older Dura Ace) or integrated with brake pad holders or the brake pads.

Thanks :) Makes sense now.