I wrote "They died after a couple months" and it was not accepted. Reported.
It would seem that "a couple of" is correct in British and American English; apparantly, "a couple months" would used only in American English. Cf. https://ell.stackexchange.com/questions/13114/couple-versus-couple-of and https://www.collinsdictionary.com/dictionary/english/couple However, if you examine Google books you will find examples of the much less used "a couple months" on the British Isles as well. Collins maintains that "a couple" means only two (which is how I learned it in school in the USA 50 years ago, as opposed to a few, which means 3-12); however, newer usage no longer maintains this distinction.
"a couple" refers specifically to "two" though, so many there is another way to say that in Dutch