Mark
What FindMyPast has as two sets of documents are in fact all one set from the National Archives WO 363 "Burnt documents".shuffled up a bit . Some are duplicates because they have been copied twice and some because, as often happens, when a man's docs were sent around the place, if they were late coming and an entry had to be made, the clerks simply started another form. If you look closely, there are four 103s but actually 2 copies of two where the one you refer to has him leaving UK and arriving France the same day. Ancestry has them in one set including some duplicates.
In army jargon, a casualty is an occurrence/event of some kind (which can also sometimes be a medical casualty), the centre column of the form shows what sort of thing is recorded there.
MaxD
