You bring up a good point: can more than one trail be run in a day?
If you run in a relatively large group, one trail per day is about what you get because the group spreads out on the trail like a big "slinky," inevitably, someone will break something, and often, too many people make too many attempts at obstacles before moving on.
If you run in a smaller group, with rigs built appropriately for the trail, many of the trails in Moab can be run in 2-4 hours. So, you can do as many as 3 trails in a day.
When we've gone as a family and taken three of our jeeps and met up with a few more--so the size of our group was 6-8 at best--we've regularly done 3 trails a day.
You can do Hells Revenge in the morning in a few hours, then grab fast food at a drive-through and do Moab Rim in a few hours (going all the way to the end at the sand hill), and then run Cliffhanger in a few hours. Then, head back to the Moab Brewery for dinner.
People commonly do Poison Spider, Golden Spike, and Gold Bar Rim in a day. This is often called Triple Threat.
People do Pritchett Canyon and then Behind the Rocks backwards in a day. I've done Pritchett forwards and backwards, and then did Moab Rim in a day.
People do Metal Masher in the morning, and then do Rusty Nail and the end of Golden Spike, and then Gold Bar Rim in a day.
It isn't as possible to take a group of more than about 12-15 rigs through trails fast enough to 3 in a day--except for Triple Threat.
RR4W run very large groups instead of splitting them up to smaller groups and then staggering them by rig/driver capability and speed preference.