It depends on where you want to see the info. The easiest is to create a fermentable called "inventory" where "origin" is used for the date and the quantity is >0. This entry will show up in an inventory report, at the top of all items with an origin field.
You can see that in the ingredients list at any time. In the supplier or notes field you could add the "post recipe" info. The supplier doesn't show up in an inventory report, though.
Alternatively, the "post recipe" info could be tacked onto the name line to see it in the inventory report. I.e. "Inventory: post Bourbon Barrel Aged Sour Durian Milkshake Double Fresh Hopped International Session IPA With Lactose and Vanilla." Then you'd be sure.