It’s not organizationally possible to enlist an exhaustive list of duties to be performed by any incumbent.

The conventional byline is “these are only illustrative and not exhaustive"

This clause should take care.

Besides it will also be a good idea to factor in certain weight -age for taking on additional assignments/responsibilities in the performance appraisal process - KRAs . This will systemically provide for an impetus to reach out of the job description framework.

At the end of the day, what governs is the work culture of the organization and the supervisors ability to garner his/her resources to extend the team work beyond and ahead.

Of course once in a while spot reward for achievements beyond the call of the Role will provide the right impetus and keep the energy level high.

Try

Mohan M Prasad