Halliday & Matthiessen (2014: 645):
In the second place, lexical cohesion results from the choice of a lexical item that is in some sense synonymous with a preceding one; for example sound with noise, cavalry with horses in
He was just wondering which road to take when he was startled by a noise from behind him. It was the noise of trotting horses. ... He dismounted and led his horse as quickly as he could along the right-hand road. The sound of the cavalry grew rapidly nearer ...
Here again the cohesion need not depend on identity of reference. But once we depart from straightforward repetition, and take account of cohesion between related items, it is useful to distinguish whether the reference is identical or not, because slightly different patterns appear.