Does the following sentence sound all right? Salescontinued to drop for ten months in a row until this May compared with the same period of the previous year.
If you refer to 'this' May - ie the May of this current year - surely you need to say 'same period last year', without the 'of', rather than 'of the previous year'.
No it sounds awful and its meaning is very unclear. Sales either drop or they don't. They can't drop compared to last year but they can be lower than last year. The sentence either means:
"Compared to the previous year, sales were lower from August to May," or; "Sales dropped in every month from August to May." Hope that's a help.