Amalgamation, Merger of Proprietorship with Company

Can now I amalagamate one Proprietorship gst registered taxpayer with one Company gst registered taxpayer with effect from 1st June 2020 but both the entity have already filled all gst returns till December 2020. If answer is yes what amount of ITC of Proprietorship business transferred to Company means ITC as on 31st May 2020 or as on 31st December 2020. Please clarify.