So when Madara was brought back as an Edo he sensed Hashirama's chakra, although they had been apart for 80 years he still remembers his chakra.
Also Hashirama sensed Madara's chakra after all that time.
When Minato is brought back as edo he senses Naruto's chakra, Tobriama also senses Madara's chakra.
Hiruzen could even sense Orochimarus chakra even though Orochimaru had stuffed his body full of 10000 cells
The point being that anyone that had someone close to them could sense their chakra and always remember it. Every chakra is unique.
So, when Kakashi first met Tobi why the heck didn't he recognize his chakra????!!!
And also if you have half a brain you could figure out that Tobi was Obito.
Kakashi thinking: "Hmm lets see, a man wearing a mask hiding his left eye, but has a sharingan that can make things disappear on his right side? Hmmm. I have a sharingan on my left side that can do the same thing, hmmmm, thats weird... Every Uchiha are dead except Sasuke & Itachi, hmmmm. Only one i can think of is that guy that fell in the rubble that we never actually saw die, hmmm. That Obito fellow, hmmm. Naaaah, couldn't be him he fell in the rubble and was never seen again"
The same goes for Minato, when Tobi attacked him and Kushina, Minato had no idea who he was, even guessing its Madara. So his bird brain guessed that it's more likely that someone that died 80 years ago is still alive then Obito surviving a stone rubble. Plus, he couldn sense his chakra?
And DONT SAY it's beacause he had Hashirama cells in him, beacause so did Madara and Orochimaru was full of 1000 different cells but Hiruzen still sensed it was him.
THIS IS A PLOTHOLE AND JUST HORRIBLE WRITING
