We expect $dateToString %w to return the values 1-7, as indicated by the documentation for previous versions:

• https://www.mongodb.com/docs/v6.0/reference/operator/aggregation/dateToString/#format-specifiers
• https://www.mongodb.com/docs/v5.0/reference/operator/aggregation/dateToString/#format-specifiers

However, the latest 7.0 docs have been changed to indicate that %w formats to 0-6, which is incorrect: https://www.mongodb.com/docs/v7.0/reference/operator/aggregation/dateToString/#format-specifiers