Just came across this recent article; very interesting towards the end:
"Tilar Mazzeo, the author of The Secret of Chanel No. 5: The Intimate History of the World’s Most Famous Perfume, says that “historically Chanel No. 5 certainly did use ambergris.” The original formula leaked in the 1930s, she says, and “the copies I have seen include ambergris or ambrein—the essential scent element of ambergris—as an ingredient.” Not so, says Philip Kraft, a German chemist who creates scents for Givaudan, a Swiss manufacturer of fragrances. “There never was any ambergris in Chanel No. 5,” he says. “Not in the formula from 1921, nor in the one of today.” A representative from Chanel declined to comment for this story."
Could the ambrein alleged to be in Chanel No 5 perhaps be extracted from labdanum?