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[Abridged] With a growing number of molecules observed in many comets, and animproved understanding of chemical evolution in protoplanetary disk midplanes,comparisons can be made between models and observations that could potentiallyconstrain the formation histories of comets. A $\chi^{2}$-method was used todetermine maximum likelihood surfaces for 14 different comets that formed at agiven time (up to 8 Myr) and place (out to beyond the CO iceline) in thepre-solar nebula midplane. This was done using observed volatile abundances forthe 14 comets and the evolution of volatile abundances from chemical modellingof disk midplanes. Considering all parent species (ten molecules) in a scenariothat assumed reset initial chemistry, the $\chi^{2}$ likelihood surfaces show acharacteristic trail in the parameter space with high likelihood of formationaround 30 AU at early times and 12 AU at later times for ten comets. This trailroughly traces the vicinity of the CO iceline in time. The formation historiesfor all comets were thereby constrained to the vicinity of the CO iceline,assuming that the chemistry was partially reset early in the pre-solar nebula.This is found, both when considering carbon-, oxygen-, and sulphur-bearingmolecules (ten in total), and when only considering carbon- and oxygen-bearingmolecules (seven in total). Since these 14 comets did not previously fall intothe same taxonomical categories together, this chemical constraint may beproposed as an alternative taxonomy for comets. Based on the most likely timefor each of these comets to have formed during the disk chemical evolution, aformation time classification for the 14 comets is suggested.

Cometary compositions compared with protoplanetary disk midplane chemical evolution. An emerging chemical evolution taxonomy for comets