In addition, bank managers also acted in complicity with rich black money holders by documenting that their currency bills were actually exchanged by multiple ordinary folk, whose IDs' copies (necessary proof for exchanging) exist in large numbers at any bank.
Now, the question you should ask is - How much of black money was in cash? The answer is approx. 6% according to Min. of Finance White paper on Black Money. So, effectively - 86% of the currency was demonetized to target 6% of unaccounted income. No matter how you slice/dice this policy, the costs significantly outweigh the benefits.
[0] http://timesofindia.indiatimes.com/business/india-business/8...
[1] https://www.bloomberg.com/news/articles/2017-01-04/india-sai...