Assortments are often more available than specific breeds are, and sometimes even bargain priced. However, no record is kept of which birds are used to fulfill assortments, I'm afraid. They are fulfilled with the breeds that hatched well that week.
To determine what you received, you can compare your chicks to the list of possible breeds and the photos on our site to try to identify them. In some cases, you may know instantly what you have received, and in others you may not be absolutely sure until the birds get their mature plumage, so it can be an exciting wait!