To me, nadsat is an interesting study in language evolution. Although the book was written in 1962, it's not intended to convey the slang of that year (or for that matter any other year). The book is set in the future and we know that slang evolves over time. Some slang words take on a meaning opposite from that of the original terminology (I'm a "bad" ass), other slang just combines words, or mispronounce them in creative ways.

No matter whether you read the book in the '60s or today, the language still seems futuristic. If you take any other book from that time period and look at their use of slang, you'll find they are hopelessly outdated.