Was not Hagoromo died after he sealed Mazo and left Indra and Ashura. At that time Uchiha and Senju clan not born yet And Hamura never sealed Juubi inside himself and he is not immortal.
Both Hagoromo and Hamura died thousand or hundreds years before Madara is born.
I am not talking about Juubi here, I am talking about the God Tree's power or more specifically the power of the fruit. One thing that it grants is immortality. The God Tree's powers were taken by Kaguya, which was then inherited by Hagoromo and Hamura, then Indra and Ashura and then Sasuke, Naruto and Hinata.
God Tree -> Kaguya -> Hagoromo and Hamura.
Hagoromo -> Indra and Ashura.
Indra -> Sasuke.
Ashura -> Naruto.
Hamura -> Hinata. Hamura gave his powers to Hinata in the Last. This is very suspicious as it mirrors how Hagoromo gave his powers to Naruto and Sasuke.
Moreover, Hagoromo was not the only one who sealed the Juubi, Hamura also played a role, which shows the existence of a missing link. Hagoromo is Yin (Moon) and Yang (Sun). What is Hamura then ? (VM me if you want to know the secret.

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My point is Hamura and Hagoromo were immortal because of thier inheritance from the God Tree. Something must have happened to turn them into spirits and thier bodies into shells. (The Gedo Mazous).
So would it be the most accurate assumption to say that whilst Hamura was alive and kicking the Gedo Statue was safe and secure inside the moon?
Yes, it was. Madara summoned Gedo Mazou from the Moon only after his death.
We understand that only someone using a Rinnegan can control it which makes a lot of sense. The only person during that time was Hagoromo. We see black zetsu trying to make Indra activate the Rinnegan but as far as we know he failed.
That's why Black Zetsu used Indra to make him awaken the Rinnegan to bypass the seal. He might have succeeded cause we did see Indra with Spiral Rinnegan.
If Indra would have succeeded at activating the rinnegan. Do you think he could have summoned the Gedo it from the moon?
Yes, he would have. Hagoromo knew this would happen eventually and left the tablet to prevent that. The tablet was a big problem in Black Zetsu's plans so he changed it to his convenience.
P.S: Most of this is all speculation, sure Kishi has given many hints but it's still not facts until Kishi actually shows us what happened in Part 3. Instead of posting Nonsense (Most people would think that without any solid evidence), I suggest you or anybody else who is interested VM me over this matter.