@oralloy,
The term
Anglo-Saxon was used to differ the "English Saxons" from the Saxons on the continent.
But since you mention "Churls" and that laws were written "somewhere around AD600", you are obviously not referring to the European continent but to the British Isles. (We didn't have churls here, and the first written law was the
Sachsenspiegel, originating between 1220 and 1235 as a record of existing customary law.
On the European continent and especially in Medieval times, the term
serf has different meanings to how you use it.
Within the Germanic tribes - to which you refer - the reasons for serfdom were war captivity or oppression, which was then passed on by birth and marriage, and the voluntary surrender, which is already mentioned in Tacitus.