Edit: As the response to another post has stated, there may be avenues opened after decriminalization to appeal convictions. Those avenues will likely vary from state to state, if they exist at all.
http://www.rollingstone.com/culture/lists/top-10-marijuana-m...
If this information is accurate then we are talking about 400 people.
> the Colorado Court of Appeals ruled that the state's Amendment 64, which legalized the possession of small amounts of marijuana, meant that some offenders could appeal their convictions. A unanimous decision by a three-judge panel agreed that the ruling should be interpreted retroactively, which immediately overturned the 2011 conviction of a woman for possession, and potentially setting the stage for the release of many Coloradans incarcerated for marijuana possession. Hundreds of prisoners and persons on probation could see their sentences modified, and some could even be released.
Quoting further from http://articles.latimes.com/2014/mar/14/news/la-ol-marijuana... :
> To start, the Colorado ruling gives marijuana prisoners the right to appeal their sentences. It doesn’t guarantee they will actually see any relief. That will have to be decided on a case-by-case basis. The ruling also does not appear to apply to older convictions, where those who already served prison time could petition the court to expunge their records.
> Of course, the ruling doesn’t apply to other states. Washington, which also legalized marijuana in 2012, like Colorado, will have to make its own provisions for retroactive ameliorative relief.
In any case, federal convictions have no guarantee of retroactive ameliorative relief.