Human spine: Is the coccyx really fused?
The wikipedia article links to two papers. The first article has data for 120 pain-free and 51 affected patients with data on the number of coccygeal segments in each. We can back-calculate a reasonable approximation of segment distributions from their percentages:


1 Segment: 7%
2 Segments: 51%
3 Segments: 38%
4 segments: 4%


So 2 or 3 segments makes up almost 90% of the population. Given that only 7% of the subjects had single element coccyxes, I think it's safe to call the coccyx usually made of multiple elements.

Whether you refer to those multiple elements a single bone if largely a semantic argument. Since there is variation, it seems reasonable to call the collection 5 of variably fused terminal vertebrae the "coccyx".

As a practicing anatomist, I would say that there are 29 vertebrae, as in 29 vertebral elements (but you can't say 29 ossification centers, because each is made of multiple centers). These fuse into 24 free vertebrae, the sacrum (5 fused vertebrae) and one coccyx, which is variably fused.