However, the mechanism mostly remained a mere hypothesis in our previous report and many questions remained unanswered. Gratifyingly though, all proposed intermediates are synthetically accessible Lithium salts which allows to study their reactivity. This represents a rare opportunity to synthetically study the reactivity of intermediates in such co/terpolymerisation processes as corresponding model intermediates in related catalyses are not easily synthetically accessible. Combined with kinetics and detailed computational studies we here present an investigation into the full ROTERP mechanism. We reveal the origins of (i) the observed monomer selection processes at the chain end, (ii) the suppression and assistance of side processes leading to O/S exchange and erroneous links as well as (iii) the role of the Li catalyst and (iv) the energetic profile of the main propagation cycle.