Manifestly has an ID field on the checklist run that can be utilized for this. You can add/edit this property (called external ID) by going to the checklist run settings.
From the checklist runs list page, choose the settings gear.
This field can also be set directly from another system, without human intervention, using a Zapier integration as well as the Manifestly API, which makes it very useful for integrating Manifestly with other systems.