I haven't had time to do a lot of research on Gerry Polci, but here are some data:
Gerry Polci, member of the Four Seasons (1973-1977, 1979-1982, 1987-1990)
While the hits for the Four Seasons had dried up in the first half of the 1970s, the group never lost its popularity as a performing act. Longtime member Joe Long stayed in the group until 1975. The new lineup boasted two new lead singers in Don Ciccone (formerly of The Critters) and Gerry Polci, who eased the singing load on an ailing Frankie Valli (who was gradually losing his hearing due to otosclerosis. Eventually, surgery restored most of his hearing).
The album "Who Loves You" became a surprise million-seller for the group, as it was the first Four Seasons album to feature lead vocals by anyone other than Valli. Gerry Polci did the majority of the lead vocals, sharing them with Valli and Ciccone. The title song had Valli doing the lead on the verses, but none of the trademark falsettos in the chorus. "December, 1963 (Oh, What a Night)" had Polci singing lead in the first verse, Ciccone in the second, and Valli doing lead vocals only in the chorus. "Silver Star" had Polci doing all the lead vocals, with Valli absent from the recording aside from doing some harmony vocals.
05/2001: "IN SEASON THE FRANKIE VALLI & THE 4 SEASONS ANTHOLOGY" (Rhino/Warner Special Products R2 74266 2CDs)