An FIC accession number is usually put on items that are “found in the collection” without any other tags or clues as to where they may have come from. Additionally, as is the case for my collections, I assign an FIC accession number to items that fall under one of the cataloguing methods that were used in the past.
FIC numbers generally tell you what year the object was found, as well as a number that is assign to show the order in which the number was found. For example, at my museum, our FIC number looks like this: FIC2014.00.01. The first number is the year the object was found, the second number (the 00) tells us that the object was not part of an accession for that year, and the last number (01) tells me that the item was the first object that was found in collections for that year. Now, if your FIC number looks like: 86FICxxx.xxx, the 86 could be the order or the date, without knowing what the “xxx.xxx” is. Hope this helps!