The dual logo Wagner/Griswold pieces were made shortly before the discontinuation of the Griswold trademark altogether in 1973. The lid was originally a Griswold design, but after the acquisition, several Griswold patterns were de-branded for use as Wagner products. So, the lid, if unmarked, could have been part of a set with the pot, but at some point glass covers had largely replaced iron on Wagner DOs, so it's not entirely for certain.