prep1-24 时间的迷惑

1.         Employment costs rose 2.8 percent in the 12 months that ended in September, slightly less than they did in the year that ended in the previous quarter.

这里比较的时间是去年9月份结束的12个月，和 the year that ended in the previous quarter.，这个 the year that ended in the previous quarter. 怎么理解？

you already answered your question

the 12 months ended in September vs. the year ended in the previous quarter.
the "year" here means a fiscal year, not necessarily starts from Jan. Any period of 12 months can be said a year.