Board Thread:Consensus Track/@comment-4912646-20150519062854/@comment-6769189-20150520161446

The one that seems to make the most sense is that the 10 Tails was originally sealed in Hagoromo and later they used 6 Paths-Chibaku Tensei.

There is also the possibility that they sealed the 10 Tails completely but Hagoromo decided to summon it back down and seal it within himself to preventanone else from accessing it. Later in his old age decided that keeping the 10 Tails body and chakra at the same place was a bad idea, so he created the 9 beasts and sent the Mazo back to the moon, and Hamura decided to watch over it.