but I can spout off obscure rules to all sorts of game like nobody's business!
Not word for word, but it's there. On the bottom of page 5 it says:
As the game goes on, Cargo Crates may accumulate at a Location that are not a Native Good (see Unload). These may be picked up by discarding two Freight Bills for every one Cargo Crate of that type to be Loaded.
'of that type' is singular, so it strongly implies that the Freight Bill cards must be matching.