When did Miles need to avoid purchasing Wescon stock to prevent triggering wash sale rules?

To understand when Miles needed to avoid purchasing Wescon stock to prevent triggering wash sale rules, it's essential to recognize that the wash sale rule prohibits a taxpayer from deducting losses on a sale of stock if they repurchase the same stock within a specified time frame. This time frame includes the sale date and extends 30 days before and after that date.

In this scenario, if Miles sold stock at a loss on September 1, 2017, he must refrain from repurchasing the same stock within that 30-day window to avoid a wash sale classification. The window would run from August 2, 2017 (30 days before the sale) to October 1, 2017 (30 days after the sale).

Therefore, to avoid triggering the wash sale rule, Miles should not purchase Wescon stock on or after September 1, 2017, until October 1, 2017. This makes September 1, 2017, the crucial date after which any repurchase would effectively trigger the wash sale rules. Hence, the correct answer is clear.