How well does OpenCellID reflect actual coverage?

Apologies in advance for questions that both (1) betrays my ignorance of cell data and (2) is perhaps unknowable anyway. As I understand it, OpenCellID data is created from open source or, in other words, user-submitted, data. For this reason, I suspect that it does not capture ALL of the cells in the world, but perhaps it’s fairly good in the US (e.g. captures 85% of all cells). Is there any documentation on how “good” OpenCellID data is? How close does it get to capturing all cells? Does its accuracy vary in certain, known conditions? E.g. OpenCellID is gold in urban areas, like NYC, but, because there aren’t many contributors in, say, rural Wyoming, it’s not particularly useful there. Is there a way to derive this (or a related) measure from the number of reports (read: the “sample” variable in the data) and its date of first sampling (read: “created” variable in the data). Thanks in advance for any help!