Well this is intresting. From Bols:
"We rate these possible, coming from
mixed sources"
Tyranid Named Characters
Unique Tyranid creatures are unique per detachment. For for example 2 Dooms, 2 Swarmlords, etc... at 2k, representing a very rare breed but something that each HiveFleet knows how to create in extremis.
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Well this is gonna be fun - bring on the double Swarmy lists!!