Complex sentence: The main block of the house reflects two, and possibly three, phases, but the specific construction dates and chronology remain uncertain, appearing to date from the late 18th century but possibly dating from the mid- 18th century.
Split into simpler sentences: The main block of the house reflects two, and possibly three, phases of construction, but the specific dates and chronology of its construction remain uncertain. It appears to date from the late 18th century, but it is possible it was built as early as the mid- 18th century.