If you purchase a given security and sell it the same day, with the closing sell trades executed as separate orders, this series of transactions will be counted as a single day trade as long as no additional purchases of that same security are executed prior to the execution of the closing sells. For example, if you purchase 1,000 shares of hypothetical stock ABC and close that position in 4 separate orders of 250 shares each that same day, this would be considered a single day trade as long as they were no additional purchases taking place in between.
Accounts that have not yet been migrated to the intraday margin standards are still subject to the Pattern Day Trading (PDT) rules and are not yet subject to Intraday Margin Deficit (IMD) calls. For more information on the FINRA rule change please review the FAQs on IMD.