Notes:

• Every Pokémon game (unless otherwise noted) has a tutorial battle with the player's rival immediatly after choosing their starter Pokémon. These battles have been ommitted. Every battle has the rival with a single level 5 Pokémon, just like the player gets.
• The Pokémon League has water in some areas. Using a fishing rod in the water allows the player to encounter a small selection of Pokémon, ranging from level 5 to level 15.
• Blue has 3 different teams, depending on which starter Pokémon the player choose at the beginning of the game. All 3 teams have the same average level, however.
• The optional fight against Blue on Route 22 has been omitted.
• The Fighting Dojo in Saffron City has been omitted.
• Pokémon Yellow greatly changes the party of many Gym Leaders to be closer to their counterparts from the anime, often including level balancing. These revised boss fights have been omitted, only the original fights from Red and Blue are present.

Observations:

• Wild Pokémon levels get rather erratic towards the end of the game. This is due to areas such as Route 22 being accessible very early in the story, and wild Pokémon levels accounting for this.
  Due to the way most Pokémon games are programmed, encounters stay the same across an entire area, with developers not able to adjust encouters for a specific patch of grass.
• Wild Dugtrio can be encountered at a very low rate in Diglett's cave. These Dugtrio have a much higher level than the rest of the Pokémon in the area, and as such cause a large increase in the average level for the area.
• Trainers located in Gyms tend to have much higher levels than trainers in the surrounding areas.
• While most Gym Leaders are higher levelled than the trainers in their Gym, Lt. Surge is slightly weaker than the trainers, due to him having a level 18 Pikachu in his party. The lowest level Pokémon that a trainer in the Gym has is a level 20 Voltorb used by the Rocker.