Certainly hard to measure, but Figure 2A certainly looks like an adherence chart.

Regardless, in RCTs we usually consider a 'intention to treat' analysis gold-standard. That means that since you are assigning an intervention in the real world, even if someone drops out, you still consider them part of the intervention group, because the same thing will happen in the real world. You can also do a 'per protocol' analysis, which attempts to measure the impact of the intervention to those that adhered, but not as important...