When Goudurix saves Abba from the canyon, the sky is dark and cloudy. The moment after, it is clear and sunny.
When Asterix is going on Vikings pursuit, in one sequence he already has the magic potion that he will receive few moments later.
Vikings are historically considered to have existed from 789 to 1100 AD. This makes the Vikings in the setting of Asterix (50 BC) about a millennium early. Although their progenitors obviously already existed, they are not considered Vikings and they were certainly not known as vicious raiders in the Roman empire, where the main contact with Scandinavia was through trade.