Question: On what border of the Byzantine Empire were the last holdouts for celebrating according the  Alexandrian Easter?
Sentence: By the 10th century all churches (except some on the eastern border of the Byzantine Empire) had adopted the Alexandrian Easter, which still placed the vernal equinox on 21 March, although Bede had already noted its drift in 725—it had drifted even further by the 16th century.
Answer in sentence: yes