I had always thought this was struck under Claudius. Not only that Claudius had a much longer reign, he was Drusus' son, closer related to him than Caligula. That said, this isn't the first time I've seen this coin attributed to Caligula. Just a common mistake or was there some legit reason behind this? Actually I had seen the other Drusus denarius attributed to different rulers as well (one with the triumphal arch). If that was minted by Claudius and not Drusus' brother, then I suppose there's a chance that the shields coin was done by Caligula, since it would be less common for the same ruler to make 2 different coins (of the same demonetization) honoring the same person/event, right?
This is a typo. After denomination, they give the struck date as 41-45 - obviously after Caligula's reign. This kind of thing can happen if you accidentally copy part of the wrong record. Trust me, I've done it before!
