So for the Meat% run you are required to collect all of the hidden pieces of meat, after hours of combing through the game we still have yet to find the last, 16th piece of meat. We aren't sure if it's even in the game at this point. So for now, we'll be removing Meat% and 100% will no longer require you to collect pieces of meat. Until the last piece of meat is found or confirmed not to be in the game this will stay like this in-order to prevent confusion with future runs.

Shouldn't the 100% require the 15 pieces we do know of to be collected though?

We'll be making two categories, 100% (No Meats) and a true 100% category, for now true 100% will be hidden until we find the last piece of meat or get confirmation that it's not in the game. Until then you can run 100% (No Meats) and those runs will stay valid even after true 100% gets confirmed.