There aren’t 138 bank notes in any of them. Even the ones that had no stones had only about 82 pieces (the ones with stones had about 20). I don’t think that’s a convincing explanation considering the inconsistency in terms of whether or not there are stones and the complete mismatch between the amount of notes advertised vs how much there actually is.

It would be pretty funny if there was some kind of scam going on here where the notes were actually being reconstructed and a small portion of each paperweight was siphoned off to support the crime (perhaps by diverting whole notes early in the shredding process). That could explain why some weights had fewer notes with rocks to make up the difference. Seems unlikely obviously in reality but there should probably be an investigation to figure out why the Hong Kong Monetary Authority visitor center is participating in fraudulent behavior.