No, /[0-9]{2} / does not match a subset of what / [0-9] {2, 4}/ matches.

/[0-9]{2} / only matches "99\x{20}", where 9 can by any digit 0-9
/ [0-9] {2, 4}/ only matches "\x{20}9\x{20}{2,\x{20}4}", where 9 can by any digit 0-9

Update: Fixed copy and paste bug in in second item.