40 weeks up fully upgrade a Legendary Cloak

[Byucknah-agamaggan (Byucknah)]

This was already commented on by a Blue and stated to not really be correct.

[News] Visions of N’Zoth Content Update Notes

Just reiterating what was said by someone else, but at rank 15, the legendary cloak will have 50 Corruption Resistance at which point you’ll be able to earn a Malefic Core each week which will further increase the resistance by 3 each time. You will have the ability to get the legendary cloak to rank 15 faster than in 15 weeks.