The 200-600Km3 of melt in the caldera is actually smaller than a lot of the prior estimates, particularly as the dome events after the formation of the west thumb caldera ~170,000 Bp, totalled about 1000Km3, and volume of west theumb itself was in the 100Km3 bracket (probably more, but under ice so not easily preserved).

One other item of note is that monogenetic basalt eruptions forming small shields in the Snake river plain hotspot track total anywhere from 0.1 to 10Km3 per eruption, with the bigger shields closer to yellowstone.
The caldera is probably a mite bouncy right about now as a result of the crustal spreading following the 1700AD Cascadia megathrust (decompressed the area preferentially S of Yellowstone centred on Dotsero (colorado)), and also the eruption of basalt into the rhyolite ponded in the caldera which is lighter & acts as an end stop.
Results are that the magma is being heated & a small (sum total) amount of gas is being added, in a manner typical of unrest @ big calderas in arcs worldwide.

Would expect the 200-600Km3 of magma in the caldera to be the bit recently heated by a basalt injection post 1700AD. Would take an injection of basalt in the 100Km3 range to mobilise enough magma to cause a dome/flow event. Quakes more likely to be a result of "Hebgen lake" type caldera rim spreading, more likely due to the deep pluton in the area close to Mt.Washburn NE of the caldera proper, still @ mid to deep crustal depths, with the area above uplifting, & the area around it spreading. In this case the transform faults outside the rim would point to the advancing pluton centre, rather than the current caldera centre where the basalt is injecting.

Have a nice day: Ag