I been collecting for 20 years and I haven't really been looking at my cels anymore. I stored them on a bookshelf piled 2-3 books on top of each other. I haven't browsed my collection in about 5 years. I was aware of vinegar syndrome years ago since the postings here, but never experienced it until yesterday. As I was browsing one of my books for fun, I couldn't smell a thing, what I noticed was one cel had tons of wrinkles on it and looked warped. I took it out of the itoya and opened the bag and Bam!!! This really pungent vinegar smell so strong it hurt my nostrils! Luckily that cel wasn't a favorite or an expensive one...so I have about 10+ cel books and I had to go thru all of them...so I opened each one and sniffed... sadly I found another cel was badly decomposing too..this one was way more obvious lots of wrinkles and like you can see vinegar moisture droplets in the bag and between the layers. Sadly this one was from Bubblegum Crash OVA one of my favorite series...and it seemed to have spread with 3 other cels from Bubblegum Crisis series in the same book and 7 other cels

were affected from the first book...they were all neighboring cells...I aired all the nearby cels or ones with a hint of vinegar and they smell better now. I'm hoping the bad cel just made the others smell bad... I ended up throwing away the two bad vinegar smelling ones. Luckily none of my "dream wish list" cels had the smell yet, but some of the affected ones cost at least 100 dollars back in the day
What I learned was it always seems to affect multi layered cels. And some of them were using cheap bags with adhesive built in...I think those were used by anime world star back in the day and some other japanese dealers. The smell penetrated to the sketch, background, and the black itoya paper between the pages
Honestly I haven't changed the bags in 15 years at least and only slit a few of them. Some of them were still in the original bag they came in..I am kicking myself for not taking care of them better... I am going to change all their bags and air them every three months ...I think I need to store them in a closet with a fan blowing out and dehumidifier going. I'll invest in micropaper too for my favorite more expensive ones.
I texted my sister who was also a collector back in the day to go check up on her books too...over all affected cels are from Bubblegum Crash/ Crisis OVA (4 total) Lodoss TV, Captain Tylor, Pia Carrot (2) and Psychic Force (3 total) ...so I hope you guys can learn from this experience of neglecting my collection...