Passetoutgrains is very confusing, and over the years, I've been quoted different rules.
The BIVB on its website says that it must be at least 1/3 Pinot Noir and no more than 2/3 Gamay (well, the first necessarily implies the second if those are the only two grapes, so duh); according to that rule, Passetougrains could be 100% Pinot Noir, which a few producers claim for their Passetoutgrains.
The official décret, however, says Pinot Noir must be >30%, Gamay>15%, and if you have Chardonnay, Pinot Blanc, and/or Pinot Gris interplanted with the others, you can include them as long as they are not >15% of the total. So under that rule, you could have 85% Pinot Noir as the legal max. The décret was published in October 2009, so it is possible that the rule prior to then was different.
One of the variations I had been told in the past was between 1/3 and 2/3 Gamay, the rest Pinot Noir.
As a practical matter, I don't think anyone is going to get penalized for having an excessive amount of Pinot Noir in Passetoutgrains.