The 10 is pretty, and the 100s show them as being issued by banks — not central banks, but private banks — a throwback to another era, and also probably representing one of the many awkward workarounds done to maintain the “one country, two systems” principle. I’ve got two versions of the 100, one from HSBC and one from the Bank of China (which is not the central bank). This must be one of the last functioning examples of private bank currency, something that to my knowledge died out as common practice in the 19th century or very early 20th century.