Question on Person Number Sequencing if Overlap

Summary:

Current client wants to retain their legacy person numbers which are separated in blocks based on country. For example, US associates have a person number between 600000000 and 640000000, Canadian associates have a person number between 64000000001 and 660000000, and Mexico associates have a person number between 660000001 and 68000000. They want the person number to automatically generate in Oracle but they want the starting number to be 620000001 which is their last value for US associates but it is not the last value of all their workers. My question is if at some point the person number generation method