completion of work to a point between Eighth Avenue and Seventh Avenue. Plans for the construction of an extension of the line to between Eighth Avenue and Ninth Avenue to provide a physical connection with the IND Eighth Avenue Line were underway. On March 1, 1927, the opening of the line was set for March 15, the third time an opening date was set for the line. Work had been postponed given the amount of work that remained to be completed. The opening of the line was about a year behind the April 29, 1926 date specified in the contract. The delay was the result of surprisingly difficult construction. The Board of Transportation had withheld retained percentages, as allowed in the contract, penalizing the contractor, and trying to incentivize it to speed up work. No retained percentages were provided to the contractor until February 1927. The Flushing Line was extended to Times Square on March 14, 1927. Eastern expansion The eastern extension to Flushing–Main Street opened on January 21, 1928. At this time, Corona Yard opened, with the inspection shed and some yard tracks available for use. The remaining tracks opened on April 16, 1928. For the 1939 New York World's Fair, the Willets Point Boulevard station was rebuilt and centered on 123rd Street, just west of where the station originally lay. Some remnants of the old station are still visible; ironwork tends to indicate where the older outside-platform stations were, and the remains of the fare entry area can be seen east of the current station. The original Willets Point Boulevard station was a "minor" stop on the Flushing Line; it had only two stairways and short station canopies at platform level. It was rebuilt into the much larger station in use today, and the ramp used during two World's Fairs still exists, but is only used during special events, such as the US Open for tennis. Express service to the World's Fair began on the Flushing Line on April 24, 1939. Currently and historically, the IRT assigned the number 7 to its Flushing Line subway service, though this did not appear on any equipment until the introduction of the R12 rolling stock in 1948. The BMT assigned the number 9 to its service, used on maps but not signed on trains. Unrealized eastern expansion The Main Street station was not intended to be the Flushing Line's terminus. While