2. Using what is normally a base note as a top note, means 1 of 2 things:
a. Creed distilled a natural oakmoss oil, and used the volatile phenolic acids, discarding the more typically familiar "basenote" aspects of Oakmoss like methyl 2,4-dihydroxy-3,6-dimethylbenzoate, 2,6-Dihydroxy-4-methyl-benzaldehyde (atranol), 3-Chloro-2,6-Dihydroxy-4-methyl- benzaldehyde (chloroatranol) and such.
b. Creed used a synthetic source of the phenolic acids, and avoided the entire distillation process of oakmoss absolute (more likely)
Neither of us know for certain which method was used to utilize only the volatile topnotes of oakmoss, but I'd be willing to bet it was (b.), as the isolates and synthetically produced homologues are readily available.
And since Atranal (2,6-Dihydroxy-4-methyl-benzaldehyde), and Chloroatranol (3-Chloro-2,6-Dihydroxy-4-methyl- benzaldehyde) are the main allergens the IFRA is ban crazy for...
...using the volatile topnotes of oakmoss, whether by synthetic or by natural isolate, as Creed did in Feuille verte, would likely pass IFRA insanity, even today, as it is the aforementioned basenote components of Oakmoss (moss de chene) that are the powerful allergens.