Comparison of the neutral and plasma observations as a function of the distance from the nucleus as observed by Rosetta and the three comet flybys (see Table 1 for references for each dataset). Top panel: neutral number density determined based on the outgassing rate and Eq. (3). Second panel: total ion number density for the flybys and electron density for Rosetta. Third panel: ion bulk velocity. Bottom panel: ion ratio between mass 19 (H₃O⁺) and mass 18 (mostly H₂O⁺ with some contribution from NH). The horizontal dashed lines represent the estimated bulk velocities for RPC-IES observations of collisionopause crossings after correcting for spacecraft charging effects. The shaded regions indicate where Rosetta, DS1, and Giotto at Halley crossed into a similar range of velocities. The ion velocities at 26P/GS were above this range during the entire flyby.