If there are that many ads on 1 page then it is obvious there probably isn't nothing of value on the page. It was made for one thing in mind.
Currently, AdSense publishers may place up to three AdSense for content units on one webpage. Also maximum of three link units and two search boxes on each webpage.
Google does not allow more than 3 ads (+link units) on each page. If there is more ads than this there might be a violation to their rules. Am I correct?
I also know about a few sites that have more than 3 ad units on a single page like HubPages.com. I have seen 6 ad units on a single page there. But, 12 are too many! can you share the link with us?
If you come across 3+ google ads blocks on same webpage with a single Google Account Publisher ID then its surely a case of 3rd party ads. 3rd party or other network get license from Google Adsense and so they get advertisers also Google Logo appears below those ads and they also allow placing of any number of ads blocks. So using of any other ad network & there contract with Google will result in display of all those ads.