To investigate the implications of insufficient creep on deformation energy of tectonic coal under hydrostatic pressure, hydrostatic single and graded cyclic loading-unloading tests and graded creep experiments under varying stress gradients were conducted, deriving the following conclusions. Coal specimens under constant hydrostatic pressure exhibit a lab-unattainable ultimate creep strain corresponding to sufficient creep. The generalized Kelvin model can roughly describe coal creep behaviour in lab. Insufficient or absent creep results in a bending-down phenomenon in the deformation energy curve when beyond 76.41% ~ 82.45% of the maximum stress. With increasing creep, deformation energy for coal samples increases by 0.29% ~ 2.79%. A correction term incorporating stress and creep strain is introduced and exhibits a slow-then-fast growth trend with increasing creep strain, stabilizing at 1 after coal specimens experience full creep or reach critical stress. Original nonlinear model approximately characterizes the deformation energy of coal in actual geological formations, providing guidance for on-site production.