Question about some sequences

[asciimoo]

Question about some sequences

[vwyu]

It looks like 'ABC[XY](000[1-9]|00[1-9][0-9]|0[1-9][0-9]{2}|[1-9][0-9]{3})' solves your first problem.

For your second problem, regex-only solution may be too complicated. Instead, you can try

import exrex

str_list = list(exrex.generate('ABC[XY](000[1-9]|00[1-9][0-9]|0[1-9][0-9]{2}|[1-9][0-9]{3})'))
start = 1500
shift = 9998 + start
new_list = str_list[shift:] + str_list[:shift]
print(new_list)