Kiwi, you were partially right. They used a filly in some of the foal scenes in The Young Black Stallion.
Since the Black was an adult horse in the first film, they only used geldings and stallions.
I have Arabians, so the making of that first movie was a really big thing for me back in the day.
Yes, In Pursuit of Honor
is based on a true story. They Hollywood-ized it to make it more interesting of course, but the essential story is true.
The last U.S. Army remount division did
take some horses up to Canada and let them go, instead of 'disposing' of them as per orders. Whether or not they were actually chased by units in tanks and military vehicles is questionable.
Makes for a better story if they were though, right?