For your query, I got in contact with Quran and Hadith centre and this is what they had to tell me:
'The matter has not been clarified as such. Although it has been mentioned in a few Hadith that they are extra purified, the way that you mentioned.
But he also mentioned that Imam Ridha (as) used to bleed after 'hijammah' I.e. cupping. What explanation would we give to that knowing blood is Najis?!
He further, added that the Question does not hold such benefit either, because it does not bring or remove any commandment from thier followers, being us!
I hope this was useful.