I saw this reference on a 1913 5C buffalo...does it relate to the NGC slab? http://www.ebay.com/itm/1913-5C-TYP...278114?hash=item43e5cdcae2:g:Mm8AAOSwpDdVCL6G
I have seen references to coins being embedded and/ or somehow else being left on tombstones as a show of respect to the deceased. However, I don't know if this answers your question correctly.
Yes, I'm familiar with that...especially veterans headstones. If you had merely met them, you would leave a penny or a nickel...if you had actually been in battle with them, you would leave a quarter or 50C. Thanks.
I've never heard them called "flat packs" either, but in the early years of slabbing they were sometimes referred to as tombstones.
Even the Mint's "flatpack" seems redundant. Why would something housing flat U.S coins be anything else but flat?
The proof sets before 1955 came is small square boxes. After 1955 they were in the flat pliofilm holders. The 1955 sets came both ways and the term "flat pack" came about to differentiate the two types (box and flat pack).