I found issues in the Poke'mon storyline thats not been finished. In Poke'mon Heartgold, and Soulsilver version a key item was removed during the recreation.

In the origional versions of Gold, and Silver for GameBoy Color. After meeting bill after that night you could trade with a past version game. Such as Poke'mon yellow Special Pikachu edition.

When going back in time you dressed as Ash. Yes the girl also had to dress as ash. But the tradeing hade restrictions. No new Poke'mon or new items that didn't exist in the Kanto region versions Red, Blue, Yellow, and Green.

But, why was the feature removed. I just came with a clue. For reasons like the ds system would go to fast for gameboy to reconize the trade, unable to connect even if ds had a ds action replay gameboy link slot, or other reason.

The game never lets you know how Bill made the time machine, or leave to walk around the past dressed Ash.

As a guess for why that is if Ash saw him self pass him. Time, and space of the game might collapse since there is only one Ash.

Lastly, with new updates on regions, and wireless connections. Why was the time machine removed? Obviously Nintendo needs money so things were cut for new features.