Hi.
Since U49, the treasure maps can be stacked. Which is great.
However that applies to all sources but the Archival Essay. These do not stack, so if having all the 6 maps from eg Solstice, the 7th Solstice Archival Essay will give you map from Greymoor instead of Solstice.
Can try it right now with the current Solstice Archival Essay.
Thanks