Welcome to the forum, Jorge.
It's a good observation, I hadn't thought about this before. It's true that in books of hours for example, the signs are all one month earlier. Virgo should be August instead of September etc.
In many manuscripts, you get the labors of the month alternating with Zodiac signs. Might this have caused some confusion in the writer? Maybe we should assume that all people knew which signs belonged to which month. But then I would object that this person felt the need to write the month names with the signs. This is not something you do if you already know them by heart.
Alternatively, the writer did know what they were doing and had something in mind like in Marco's example. In that case, writing down the main month may have been required.
It's a good observation, I hadn't thought about this before. It's true that in books of hours for example, the signs are all one month earlier. Virgo should be August instead of September etc.
In many manuscripts, you get the labors of the month alternating with Zodiac signs. Might this have caused some confusion in the writer? Maybe we should assume that all people knew which signs belonged to which month. But then I would object that this person felt the need to write the month names with the signs. This is not something you do if you already know them by heart.
Alternatively, the writer did know what they were doing and had something in mind like in Marco's example. In that case, writing down the main month may have been required.