How to input date that class enrollment was completed?

Hello,

We have a standard certificate -> course -> offering -> class setup.  The offering is an On-the-Job/Practical offering, with a start date, and no end date, because the learner takes the training informally, on no specific date.

After the learner has taken the training, the OLM Admin updates the enrollment, and the certificate takes the completion date as the date the OLM Admin updated the enrollment.

The issue is, it may be a number of days after the training before the OLM Admin updates the enrollment to completed, and they would like to be able to specify the date the class was completed, so that the certificate reflects the date the training was taken.