import re

pattern = r"\b([1-9](?:\s*[0-9]){3})\s?([A-Z])(?i:\2*)\s*([A-Z])(?i:\3*)\b"
strings = [
    "1 2 3 4 Alpha Bravo",
    "1234 Alpha Bravo",
    "1234A Bbbbbbbc",
    "1234Aaa Bbb",
    "1234Aa Bbb",
    "1234A BbbbbBbb"
]

for s in strings:
    print(re.findall(pattern, s))