The described issue is standard functionality according to TUPE legislation, as the employee is/was employed according to their continuous start date and not their appointment start date.
If you wish to adjust the holiday entitlement to be in line with their appointment start date rather than their continuous service date, you will need to manually adjust their holiday history record.
Adjust the Holiday Year
If you wish to force the holiday year to calculate based on their appointment start date, follow these steps.
In the Absence zone, click Absence, then Holiday History.
Open the impacted employee record.
Open the impacted holiday history record.
📌 Note: This should be the holiday year in which their appointment start date falls.
On the details tab, tick the Do Not Recalculate option.
Change the Holiday Year Start field to match their Appointment Start Date.
Click Save.
Untick Do Not Recalculate., then click Save.
The holiday year will now be considered to start on their appointment start date, and as such, will be pro-rated based on the date entered rather than their continuous service date.