I don't understand how its not practical. Like I said, the time and date of each transaction will be recorded so that will be part of the transaction itself, showing/explaining the price it was sold for at that time period. If you say that its for the reason that it will leave a lot of Pokémon unsold then that means you're trying to cover up the truth behind those sales that ALREADY happen for the sake of every Pokémon getting sold. I actually think of it in a different way. That the only Pokémon that would be left "unsold" will still sell but as either dex or story Pokémon since better Pokémon will be available for everybody.