Hiya Tim,
I might suggest taking your stock numbers and placing them at the front of your descriptions with a dash between to separate such as:
FLB126 - Box of 12 chocolate candies.
The reason I say this is because PayPal (and some of the other payment processing sites) only allow so many characters to be submitted and many times their emails to the shop owners to give you the order from a customer doesn't show the entire field. It will many times get cut off and that could cause an issue with not knowing exactly which item a customer ordered if there are variations.
Get your stock number and the variation difference into the beginning of your descriptions for best results on the return emails from the payment processors and you'll not have issues with that then.