Hi,
Personnel number is specific to country assignment. Hence, for each country, you need a different personnel number.
All personnel numbers are linked by Person Id. All these numbers can be either generated by SAP or manually entered. It depends on your configuration.
If you wish to maintain legacy personnel number in SAP for certain validation, I would recommend you to use IT0032 or create subtype of IT0105.
I hope this helps.
Thanks and regards,
Vivek Barnwal