There is not enough information to draw that conclusion. Anyone familiar with academia (or even a R&D tech project) can imagine what could take 3 years: ethics board approval, getting permission from the relevant government agencies, finding and hiring local Rhino experts to do the tagging, iterating on design of the drill and placement of isotopes, waiting to find enough rhinos that fit the high-standards demanded for a POC study (extra large, extra healthy, etc), and so on.

Or the other way: If it really took three years to tag 20 rhinos with everything working at full speed, don't you think the University and the researches themselves would be the first to realize this is impracticle? Don't you think the journal reviewers would point this out?