Of the 12 prints in the set, only the December print has an artist's seal, which reads "Shotei". Clearly, all of the prints in this set were from the same hand. The various design elements in each print are stylistically consistent with Shotei's work of that period. Therefore, I am comfortable attributing the unsigned/unsealed prints to Shotei.
In the absence of any contradictory evidence, I am giving publisher credit to Watanabe. I'm not aware of Shotei having worked with any other publishers during this period.