I agree with your study insinuating that the project was completed after Herod's days. With that said, before the top was finished by the successors, the base of the wall had to be built. According to all sources, Herod began the work, and I have no doubt (...) that he started form the bottom. The base of the wall, where these coins were found, was built in Herod's days. The coins were dropped down there later.
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