Borrowing from Providence Perfume Co.:
"An Ode to Oakmoss...
Hello you sticky brown thing! You lichen you! How have you been? I'm sorry I ignored you all summer. You just weren't what I was looking for. My fingers rummaged through bottles and bottles of botanicals searching for just the right ingredients to make light summery perfumes: sparkling citruses, bold florals, green cool herbals and you were not desired. You were pushed to the back with your estranged sibling angelica. You were too deep and mossy and dark. But now, with the temperature falling along with multicolored leaves, you are just right."
I think the context here is unique and revealing...from a perfumer's nose and mind. However, I believe that Oakmoss is not seasonal, as someone who loves Oakmoss both as a note and as a fixative. Two cases in point I would like to mention are YSL Pour Homme and Eau Sauvage. Vintage bottles have wonderful, deep aromatic citrus compositions with herbs, spices, wood, vetiver and light florals - brilliance in both, but of course, each a very unique and historical fragrance. However, (and I would rather actually expound upon each separately, but for the sake of focusing on Oakmoss as a key missing note in current formulations of both) they are remarkably different today. The latest version of YSL Pour Homme no longer even has Oakmoss as a listed ingredient. I have recent juice from about 7 years ago of YSL Pour Homme - it was reformulated and still a very light touch of moss, but vetiver is the key base note...along with sandalwood, cedar, patchouli and a nice musk (that isn't totally clean). Eau Sauvage (from a reformulated bottle of a few years ago) was able to keep the freshness and wonderful hedione with the sparkling citrus and nice sharp herbs...and the base kept a light note of the maximum .1% of Oakmoss, had some nice damp tree moss, but is definitely shorter lived. The vetiver, sandalwood, light musk, green patchouli and amber do not last much. What was once a deep and gorgeous scent has been reformulated to a light Eau de Cologne strength bottle. I do not get great longevity with Vintage Eau Sauvage - but the depth of scent is so noticeably lighter. I do not judge brilliant and timeless compositions based on longevity typically, however...here, the missing fixative quality of Oakmoss both shortened the time you had with it and also the gorgeous richness that it used to offer. I will still wear Eau Sauvage and even layer current formulation with some precious Vintage...for, I refuse to let the memory go. Today, those of us who loves these scents seek out Vintage bottles for a reason.
'Twas the magical ingredient for so many decades of scent...opening noses of world to Guerlain's creation - Mitsouko. The aromatic fougeres were born with the fern in mind (for freshness) - but the damp Oakmoss was essential for the depth and fixative quality. Chypres cannot exist without moss, either. Scent, as a whole, will never be the same without it. And, the fact that IFRA banned Tree Moss as well effective 1/1/13...well, maybe the Mayans were right after all.
I have too many favorites to list, but wanted to mention the noticeable difference (for those of us who know, it is rhetorical) between two wonderful masculine aromatic citruses that have been forever altered. And, from a scent lover's perspective (mine) - how it differs from a perfumer's perspective. Oakmoss is a key ingredient in scents year-round, not just fall & winter...