Possible Clues:

• Not fully cooked, more time needed
• It's rare to find less than 500 + 1 like this
• It's rare to find this not performed enough
• Loser finding new energy for finish - that's rare
• Rare meaning, 'socially acceptable', is here in dictionary
• It's rare to find this less than five centuries and one
• Not sufficiently cooked
• It's rare for this to be so unfinished
• It's rare for this not to be performed enough
• 'It's rare to find it like this, as a matter of course (9)'