Use relevant agreements, schedule changes, payroll and employment records that identify the actual arrangement. Reconcile differences rather than relying on the current job title alone.
Show when the terms actually changed
A later letter calling the role permanent does not necessarily establish earlier full-time work. Explain the effective dates and duties with records appropriate to the facts. Where the transition happened gradually rather than on a single date, show the incremental steps through payroll or benefits records rather than presenting the change as though it occurred all at once, since an averaged description can obscure exactly when full-time duties actually began.
Identify whether the change was requested by the employer to meet a growing need or initiated by the applicant, because the reason for the change can itself help explain why the role's knowledge requirements expanded alongside the hours. Reconcile any benefits enrollment, tax withholding, or scheduling record that reflects the earlier reduced arrangement, since a record still showing the old schedule after the claimed change date invites questions the explanation should address directly. Keep the description of duties tied to the same effective dates used in the payroll history, rather than describing responsibilities in general terms that could apply to either period.
A title change recorded only in a personnel system, without a matching adjustment to pay or hours, explains very little on its own.