Mystery of the Fake USD Notes

At Rurrenabarque, a cowboy town at the fringe of the Bolivian Amazon Pampas, we discovered 2 pieces of USD100 and 1 piece of USD20 fake notes in my money belt. It was quite a blow to us as we might be running out of money soon without that USD220!! Luckily it was almost towards the end of our trip already so we just had to be more careful with our spending.

How did the fake notes get into my money belt in the first place?!! There were too many suspects. From the Bolivian money-changer? From the Peruvian money-changer? From our Malaysia money-changer? Someone broke into my bag to exchange the real notes to the fake? But the 1st two deductions can't be true because the largest notes we had were the 100 dollars denomination. So we'll never get any change in 100 dollars. And if we were to get fake notes, it would have been in the local currencies since we only change USD to local currencies, not the other way around. So it's down to 2 suspects, either someone exchanged it, or it's from the Malaysia money-changer.

I recalled that I left my rucksack at the tour agent locker before we left for our Amazon trip, with my money belt discreetly hidden among my dirty laundry and all other stuff. (we were not encouraged to bring valuables with us to the Amazon because the door to our shared room cannot be locked)
When I came back and retrieve my rucksack from the locker, the padlock(we used our own padlock) was still intact and my bag looked untouched, like the way I left them. So I really didn't think someone had picked the lock to exchange my genuine USD notes to fakes.

So we only left with the last suspect - the Malaysia money-changer. But the Malaysian money-changer was a trusted one that Chris's dad has been using for years! When I went to see them, they pointed out to me, on the notes itself, it's already printed with the words 'SAMPLE' in Spanish, just that we didn't recognize the word. And to be honest, the notes really looked and felt VERY fake. The money-changer told Chris, 'Why would I want to cheat you? I still want to run my business, and I've known your dad for years. If I really wanted to give you fakes, I would have given you one which looks more genuine, and I won't even print the words in Spanish. How would I know you are going to Spanish-speaking country in the first place?'
Well, that made sense. So they can't be the culprit either.

I was left with noone else to blame. I tried to recall all the incidents involving money in my trip but the more I thought, the more I was confused. I 'kind of' imagined that I myself picked up the fake notes from somewhere thinking it's real and I secretly slipped it into my money belt, or another 'possible reality' was someone gave me the samples for fun, and I accepted it and forgot to remove it from my money belt. I really cannot remember whether these are just hallucination or reality, blame it on excessive intake of oxygen that made my mind go bonkers. (we travelled from an altitude of 3700m down to sea level in 1 day)

When I came back home to Malaysia, I still couldn't believe we've been cheated off USD220 so I reconciled all my spending with the total amount of money I brought with me. Well, surprise surprise! It actually tallied! That means I did not lose USD220 at all?!! These fake notes were just extras afterall?!

Did someone played a practical joke on me?! Where did that USD220 fakes come from then?! Until now I still haven't got the answer... I guess some mysteries will remain unsolved forever...