These orbital parameters are usually expressed either by Keplerian elements or by State Vectors. State Vectors represent the 3-D Position and Velocity components of the orbital trajectory at a certain snapshot in time or epoch .
Keplerian elements are descriptive of the size, shape, and orientation of an orbital ellipse.
Vectors can use an Earth-Fixed reference frame, with the epoch time expressed as an offset to the Launch date and time. Complete sets of Keplerian elements are valid only for a specific Launch time. Therefore, pre-Launch Keplerian elements have limited usefulness. If the Launch time changes, updates need to be made before the elements are useful for orbital predictions. A time-independent State Vector can be readily combined with the Launch date and time, using software such as VEC2TLE, to produce a valid set of Keplerian elements.