If they were scamming you, wouldn't it be a bit silly to use the same tracking order as they used for a previous order, or am I missing something? 

What I'm saying is that if it's fairly easy for you to prove they've applied the same number to two separate orders, they're not likely to try and scam you by using that number twice (unless they're pretty dumb).  If you can't prove they've used it for two different orders that's a whole different story, but if you can, I'd say that they've got mixed up somehow and put the wrong number in.  In that case you can hopefully get it sorted.

I buy a lot from overseas (not China or Asia) and most of my orders are from one particular place.  They've never ever given me a tracking number and I've sometimes wondered how I'd handle it if something didn't arrive.  I spent $900 last week and my order will come in two boxes.  I asked them to insure it and add the charge to my total bill, but a lot of these places are really busy and I don't know whether they'll do it.  It should only take seconds to add the extra charge when they print the label. 

Even though they don't notify customers of tracking numbers, they may keep a record of them, but I don't know.  They're really good in other ways so I can only assume they've never thought of supplying tracking numbers.  It might pay me to ask them about it one day.  I'd hate to have to make a claim against a place I want to continue trading with.