The correct answer is: A. were/were dated.
The oldest Mesoamerican calendar inscriptions were found at the site of San Jose Mogote in the Oaxaca Valley. These inscriptions date back to 600 BC. The inscriptions are made up of day signs, which are symbols that represent different days of the month. The day signs are arranged in a specific order, and each day sign has a different meaning. The inscriptions can be used to track the passage of time, and they can also be used to predict the future.
The other options are incorrect because they do not accurately reflect the information in the question. Option B is incorrect because the inscriptions were dated to 600 BC, not 600 AD. Option C is incorrect because the inscriptions are not dated to the present day. Option D is incorrect because the inscriptions have already been dated, and they will not be dated again. Option E is incorrect because the inscriptions have already been dated, and they will not be dated in the future.