Can I extend my stay in Thailand until my stamped exit date of August 3 even though my flight is booked for July 3?

An Indian citizen arrived in Thailand on June 5 with a confirmed return flight on July 3. The stamped exit date at immigration is August 3. They are seeking to extend their stay in Thailand and want to know if they can stay until the exit date or must leave according to their flight schedule. Comments clarify that the flight schedule is not important and that the individual can stay until the exit date stamped in their passport, which is August 3.