There are flashbacks, done with "home movies". Some were created for this movie, and some are footage of Philomena's actual son.
Several decades later, partly due to the original book, it became apparent just how common stories like Philomena's were in Ireland before, during, and after the 1950s. Revelations about widespread forced adoptions, and abuse of children and unmarried mothers by the Roman Catholic Church, have given this movie a much darker undercurrent than originally intended.
In the United States, the M.P.A.A. gave this movie an "R" rating for ambiguous usage of the "f-word" (usually, only one non-sexual utterance of the word is permitted for "PG-13"). A lengthy appeals process ensued, with producer Harvey Weinstein and writer, producer, and actor Steve Coogan testifying at the hearings in Los Angeles. The Weinstein Company won their appeal for "PG-13" on November 13, 2013, nearly a week before the scheduled theatrical release.
When Philomena Lee (Dame Judi Dench) is asking Mary (Mare Winningham) if Michael (Sean Mahon) ever talked about Ireland, she comments "no, not really" . In the book it is stated that Michael and Mary return to Ireland and talk to the nuns about finding his mother.
At the beginning of this movie, when Philomena has sex at the fair, the camera pans down to an apple with a bite taken. It's a not-so-subtle reference to the original sin.