Recently on my SMP server, I had been having issues getting a Fortune 3 Enchantment on my diamond pickaxes even after 40+ enchant attempts. I decided to go into a creative world and enchant two inventories worth of diamond pickaxes to test and see why that was, seeing as I had never had this issue in previous versions of the game. My results are recorded below:

Single Enchants:

• 15 Efficiency IV
• 4 Efficiency III
• 4 Unbreaking III
• 1 Fortune II
• 1 Silk Touch

Double Enchantments:

• 17 Efficiency IV, Unbreaking III
• 11 Efficiency III, Unbreaking III
• 7 Efficiency IV, Fortune II
• 2 Efficiency IV, Silk Touch
• 2 Unbreaking III, Fortune II
• 1 Efficiency IV, Fortune I
• 1 Efficiency III, Fortune II
• 1 Efficiency III, Fortune I
• 1 Efficiency III, Silk Touch

Triple Enchantments

• 2 Efficiency III, Unbreaking I, Silk Touch
• 1 Efficiency IV, Unbreaking I, Fortune II
• 1 Efficiency III, Unbreaking I, Fortune II

After 72 enchantments, not a single pickaxe returned a Fortune 3 Enchantment, and as the number of enchantments increased, the strength of the individual enchantments decreased significantly. These percentages don't match up in any way with the information given on the official Gamepedia site nor my own experiences in the past.