Is the marriage contract considered valid if the offer and acceptance were not explicitly stated, and the imam sufficed by saying: "So-and-so has married so-and-so," to which the attendees responded with "Yes"?

Marriage is only valid with offer and acceptance. The offer comes from the wife's guardian (wali) or his agent, and the acceptance comes from the husband or his agent. The offer is made by the guardian saying: "I give you my daughter so-and-so in marriage." And the acceptance from the husband is: "I accept." It is permissible for a single agent to conduct the contract on behalf of both parties, by saying: "I have given so-and-so in marriage to so-and-so." If the authorized official (ma'dhun) says this as an act of creation [of the contract], the marriage is valid. However, if he says it as a statement of information [reporting a past event], it is not valid, and the contract must be re-done with the correct wording in the presence of two witnesses.