So let's look at a few misconceptions. Often in understanding International Business you have to unlearn many things first, much of the information out there particularly is inaccurate or worse dangerously ambiguous.
Traders are better off NOT using documents like LOI, ICPO, FCO, etc. Even if and when they rarely are used in internal trades, on a restricted level within specific industries, they have no legal or customary basis in International Trade whatsoever. In fact the presence of many of these terms are considered to be signs of Advance Fee Fraud, by knowledgeable players and law enforcement.