question about butyl on corner edges

[xscorex]

Ok when I pulled my corners apart on the back. there was butyl between the two skins, the butyl under the j rail. Now Im totally confused as to how to put it back together. I was using a few small nails to hold it in place. Should I nail the edges or staple them then run butyl under the j rail? or do I need butyl under both?

[Redwings]

When we did our compact we put butyl between the two edges as well as under the j-rail.

[Redwings]

P.S. We also tacked in a few small-headed nails to hold the top edge in place over the first layer of tape. Then we laid the 2nd layer of tape on and installed the J-channel.