DL is the marketing carrier and therefore DL's rules apply. DL does not use MSC and therefore MSC is irrelevant.

Both VS and AF check-in agents will see this on their screens at check-in and your e-ticket receipt should show this as well. While there are occasions when this can be an issue, within ST, it won't be.

Thus, 157 it is. Most likely they let it slide, but the better practice, given the exorbitant cost of excess baggage, is to use a bag which you know will not be an issue.