import calendar, re

months_abr = "|".join(calendar.month_abbr[1:]).lower()
months_exp = "|".join(calendar.month_name[1:]).lower()

pattern = fr"""
(?<!\d)
(
  (?:\d?\d[./])?\d\d(?:\d\d)?
  |
  (?:{months_abr}|{months_exp}) [\s./-]? \d\d(?:\d\d)?
)
\s*(?:-|to)\s*
(
    (?:\d?\d[./])?\d\d(?:\d\d)?
  |
    (?:{months_abr}|{months_exp}) [\s./-]?\d\d(?:\d\d)?
  |
    current|present|(?:un)?till\s?-?(?:date|now|date)|to\s-?present
)
"""
text = r"Google, Inc 09/19 - 09/20 CA, USA\n3/2006-6/2007\nsss 2017 - present (or) 2015 - 2018 sss"
find_all = re.findall(
    pattern, text, flags=re.VERBOSE | re.IGNORECASE
)
print(find_all)