If there are no dates, then it is most likely a calendar year end 1041.
Another way to verify this is to look at the year printed in the middle of the top of the K-1. If it is anything other than the current year (2016), then it is probably a fiscal year unless the return was filed late; which could mean you would need to file an amended return.
*A reminder that posts in a forum such as this do not constitute tax advice.
Also keep in mind the date of replies, as tax law changes.
