The Gibbsian surface excess (GSE) can unequivocally measure the extent of adsorption of a gas on a solid adsorbent. A differential iso-excess heat of adsorption based on the GSE thermodynamic framework provides a physically and thermodynamically consistent description of the adsorbent heterogeneity or homogeneity. The actual amount adsorbed (AAA) cannot be experimentally measured. It must be estimated from the experimental GSE by making extraordinary assumptions regarding the nature of the adsorbed phase. Thus, the AAA is a model dependent variable. A differential iso-steric heat of adsorption based on the AAA thermodynamic framework can be misleading and artificial. The NET amount adsorbed (NAA) is an experimental variable. It is also directly related to GSE. Thus, it provides no further insight into the adsorption system vis a vis the GSE. A differential iso-NET heat of adsorption based on the NAA thermodynamic framework can be misleading and fictitious.