Phew, just finished rebasing the cavalry for my Ancient British/Gallic army. They certainly show the gradual evolution of the army from it's origins over 40 years ago.
The light cavalry is the oldest and is made up of various conversion by adding Airfix ancient/medieval torsos to US cavalry legs and horses, then over the years a few more variations were added.
Extra units were added when figures became available, the noble heavy cavalry on the right started out as Italeri Roman Republican cavalry. Those on the left are the armoured figures from from Hat Celtic Cavalry
The Gallic medium cavalry are a mix of all the above plus the Italeri Celtic Cavalry.