Taking a look at the earnings calendar on the Nasdaq site I stumbled upon the column "Fiscal Quarter Ending". I see that some companies that report earnings on the 21st of November (http://www.nasdaq.com/earnings/earnings-calendar.aspx?date=2017-Nov-20) have different fiscal quarter endings.
Let's take for example the following 3 rows:
Agilent Technologies, Inc. (A) whose fiscal quarter end is at Oct 17, in that case is the quarter they're reporting for is Jul, Aug and Sep?
Amtech Systems, Inc. (ASYS) whose fiscal quarter end is at Sep 17, in that case is the quarter they're reporting for is Jun, Jul and Aug?
Northern Technologies International Corporation (NTIC) whose fiscal quarter end is at Aug 17, in that case is the quarter they're reporting for is May, Jun, July?
Why do stock markets allow these differences in reporting?