Indeed, this convoy has made a variety of seemingly contradictory impressions on those reporting. The strongest possibility may be that the reports we're receiving aren't very accurate.
We don't they just count the vehicles, I would imagine even basic computer vision software could do that with reasonable accuracy.
If 100 vehicles are in a 10 mile long convoy and then they space out more and are now in a 20 mile long convoy, it's still 100 vehicles.
I do enjoy reading each day the different lengths and distances to Kyiv.