As we will see in the next chapter,the use of both the new reflexive with self and old ones without self continues for some time. The actual change involves the old english adjective self being reanalyzed by learners of Middle English as a noun with a possessive
My or thy. The third person has an accusative pronoun him before self because it changed when self was still an adjective modifying a pronoun.the first and second person reflexive were formed when self was a noun , so my ,thy ,our,and your are possessives.