Extra Bones

So my issue is when I’ve bought characters from the marketplace, if they share the Epic Skeleton it’s a simple case of right clicking the character and assigning it to the UE4 default Skeleton, this means I can use all the same animations I’ve already put together etc, it makes life so much easier.
But sometimes a character i’ve bought will have the same skeleton but there might be some additional bones. Whenever there are additional bones when I try to assign the skeleton it’ll tell me bones are missing and fail to assign it. I spoke to someone about buying their character and they told me that even if there are extra bones so long as the main bones are all the same then it should work. I’ve tried looking into this further to no avail.
Which is the truth? am I doing something wrong and it should assign or are they wrong? all I know is even if there is ever one extra bone I can never assign it.

Any help/information would be appreciate greatly.

You need to use retargeting to get the animations that work on the base epic skeleton to work on the skeleton with extra bones. it’s as simple as that.

Everything you need to know is here.

Base concept is as long as your main skeleton does not change then additional bones can be added as long as the main hierarchy does not change with additional bones added as children off the hierarchy.When imported the bones are added to the target skeleton as added or virtual bones and any animations applied to that addition will be recognized.