Is it difficult to remember scents?

Like if I try to think of a scent I can never fully replicate the scent profile on my mind
Not fully no. But thinking about a fragrance that impressed me before, I can recall enough of it to partly remember how it smelled, and decide whether I should smell it again or buy it. Obviously a memory is not the real thing. Duh

like I can very accurately do with an image, or a tune for instance
I'm convinced that your memory of images and music are not accurate either. Unless you have a photographic memory, absolute hearing or are a highly trained professional with great memory. OK, I admit that a simple tune can be remembered accurately because it contains much less complexity than an image or a complex scent. Also, I think that some fragrances are sufficiently simple so that a trained perfumer can recognize what's it made from and reproduce it (See the BBC documentary for that).

like what if for any reason I can't use X perfume anymore, I think I would have trouble remembering it without the re-experience
True. But when you try to remember and focus you might get -roughly- the scent profile back in your mind, even when it's not the full picture. Other times another scent may trigger the memory of the perfume.

Good luck with your N°5 dilemma

There are certain perfumes I wore years ago, and I can still smell them, in my memory. The fragrance will only come to my mind, when I am reminded of the perfume, or I have written about it. For example,I saw a picture of KL, a fragrance I wore a lot in the 80's, and straight away I could recall how it smelled. The same with Opium, and Estee Lauder Youth Dew...which I can recognize in an instant. Not all fragrances have the recall..but somehow, these ones are inbedded in my memory!

Snap. I saw the Bijan bottle on the homepage and suddenly Black and then Nude came to me in memory. I always remember my Mother in law in a cloud of Je Reviens, the good stuff, I hasten to add.

What you're asking is that is it difficult to be a walking encyclopedia of all the fragrances you've worn or smelled. Answer: yes. However, it's no more difficult than being a walking encyclopedia for every song you've ever liked, every outfit that you worn, every building you photographed, and so on. Most cultures are throwing information at us so quickly and in such amounts that it's a wonder anything can be recalled by anyone at all.

If asked, I couldn't remember a scent per se. I could remember the images it evoked for me, but as for remembering the actual scent, not at all. I can remember the feeling it brought, how it made me feel and all that, I could describe what it smells like perhaps if I truly found the perfume remarkable, if it was one that I really enjoyed.