She forgot. Sometimes the dustbag gets separated from the bag and they don't notice. In that situation they will often give you a generic one and hope you don't notice. If I catch it when I buy the bag I ask them to take the dustbag from another bag of that brand.
What a great forum! I also just bought a new Valentino handbag and it came with a white dust bag (no logo or markings). I called and checked and she said she would get me the *right bag* and have it waiting for me when I return on Saturday.
Not sure of the season, but this bag is GORGEOUS! LOVE!!