This juice has definitely changed. I received a 100ml bottle for christmas in 2013 and it was fantastic. Very smooth, sweet, raisin-y, graham. I still have ~15mLs of that bottle. I've ordered twice since then, once in 2014 and once earlier this year, and both of them were much more harsh, less sweet, no raisin-y taste, and lacked the 'smoothness' that my original bottle had. It is not a case of mistaken memory. I still have the 2013 bottle and drip from it occasionally.
My assumption is that Ben was using something that had a fair amount of diacetyl in it without knowing it. Once he found out, he asked the manufacturer to produce that flavor without the diacetyl. He has technically never changed the recipe, as it's the same flavoring from the same vendor. However, as a DIYer, I know very well that removing an ingredient like diacetyl or any of it's related diketones will change the recipe drastically.