Extra 2,000 men in Minard’s drawing?

My wife and I were looking at the large print of Minard’s depiction
of Napoleon’s march to Moscow (Tufte, Visual Display of
Quantitative Information [second edition], p41), and noticed that
on the return trip, near the end, the army’s size apparrently
swells from about 12,000 men to 14,000 before dropping once
again to 8,000. However, we see no indication that a 2,000
person contingent has joined the army.

What’s going on here? I’m fairly certain that I’m not the first to
notice this oddity, but I’m at a loss to explain it based solely on
the text.