In "Pilot", it is mentioned by Lex that the mansion was shipped from Scotland stone by stone and Clark says that he remembers that the trucks were rolling by for weeks. However, in the flashbacks in this episode, the mansion is seen just days after the meteor shower and looks much the same as it always has and there seems to be no construction going on anywhere.
Young Lex tells Davis that the box was forged from the armor of St. George. Lionel told him this story during his 12th birthday party in "Memoria". The flashbacks seen here in "Eternal" happen directly after the meteor shower, making Lex nine years old and already knowing the story.
The guards chasing Davis in 1989 were armed with Heckler and Koch MP7s, which were not put into production until 2001.
Davis's foster record birth-date is a few months after Clark's. Lex is about seven years older than Clark legally, so Davis would still be a toddler around 3-years-old, as Clark was, at this time.