The inline pod for Data-Tumbler states that the license is same as perl, i.e. GPL version 1 or later or Artistic 1. The new LICENSE file reiterates that the license is same as perl, but incorrectly then refers to GPL version 2 or later rather than version 1 or later. It might also be more appropriate to ship a copy of GPL-1.0 rather than GPL-2.0 as a separate license file. Same applies for Test-WriteVariants.