Poseidon was actually modeled in 1974, but De Lue occasionally put the wrong date on the wax during the casting. See pages XI thru XIII of “The Sculpture of Donald De Lue / Gods, Prophets, and Heroes” by D. Roger Howlett regarding issues concerning dating of sculptures.
“This work was modeled in 1974 and immediately put forth as part of a fountain for a proposed Philadelphia commission. The god of the sea springs from the tails of five diving dolphins” from D. Roger Howlett “Donald De Lue: Gods, Prophets, and Heroes,” 1990, pg. 112.