In most instances, airlines maintain consistency in their flight numbers, meaning that a specific flight number generally denotes the same route regardless of the day.
Using consistent flight numbers for daily or regularly scheduled flights helps minimizing confusion for passengers and staff. In cases where the same route has multiple daily flights, the airline may assign different flight numbers to each departure, which remain consistent across days.
However, there are exceptions where flight numbers can indeed change for the same route on different days, largely due to such factors as day of operation (flights that don't operate daily may have different flight numbers based on the day of the week), seasonal changes (a flight number used for a route in summer may not be the same in winter), and higher demand (additional flights on the same route may have different flight numbers).