Spectra of sub-millimetre HCN laser transitions within the Coriolis-coupled system observed in six to eight epochs towards IRC+10216. Spectra are presented from left to right for the following transitions: (a) the (0,4⁰,0), J = 9−8 line at 805 GHz; (b) the (1,1^1e,0)–(0,4⁰,0), J = 10−9 line at 891 GHz; (c) the (1,1^1e,0)−(0,4⁰,0), J = 11−10 line at 964 GHz; (d) the (1,1^1e,0), J = 11−10 line at 968 GHz; and (e) the (1,1^ee,0), J = 12−11 line at 1055 GHz. The Herschel/HIFI spectra are plotted in red, while the SOFIA/4GREAT spectra, smoothed to a channel spacing of ∼0.15 km s⁻¹, are shown in black. The observing dates are labelled in their respective panels. In each panel, the vertical dashed blue line indicates the stellar velocity of −26.5 km s⁻¹, the vertical blue bars mark the terminal velocity of ± 18 km s⁻¹, and the horizontal dotted blue line represents the baseline. The grey-shaded regions indicate the velocity ranges used to determine the integrated intensities.