Two companies partnered on a biomedical project and formed a joint venture (AVT). They signed a letter agreement on April 9, 1999 to buy and sell stock in AVT. One party later claimed the other hid important information before the deal closed on June 1. The court ruled that once the April 9 letter was signed, it was a binding final agreement, so the other party had no duty to disclose new problems discovered between April 9 and June 1. For subcontractors, this means preliminary agreements can lock in your rights earlier than you think.
A letter agreement or preliminary deal can be legally binding and final, even if you thought more negotiations were coming. Don't assume you have time to back out.