"Last January" vs "January last year"

> He arrived in New York last January.其中的last January
> 书上解释为今年一月，而不是去年一月~困惑~
> 如果按这样翻译那last该怎么分辨是今年还是去年？

This is a commonly confused word for Chinese. "Last" means the latest past. So if it's any month after January now, "last January" means January this year. If it's February now, "last May" means May last year. If a Chinese textbook says "last" in "last [month name]" always means "last year", or "last" in "last [day of week]" means "last week", it is wrong!