I suspect that result has more to do with the transferred use of 'odyssey' to mean a long, wandering adventure, which seems to have appeared in the late 19th century. The Oxford English Dictionary has the earliest attestation of that usage being from 1886 ( R. L. Stevenson Kidnapped xxvii. 284   This is a great epic, a great Odyssey of yours.), so that would fit the beginning of the upward curve on the graph.