What time did Flight 175 take off?

According to the Bureau of Transportation Statistics, United Airlines Flight 175 took off from Boston's Logan Airport at 8:23 a.m, as this is listed as the "wheels-off time."

This data is published in my last post:

http://ningens-blog.blogspot.com/2007/03/flight-11-and-flight-77-now-in-bts.html

However, the 9/11 Commission Report states that "United 175 pushed back from its gate at 7:58 and departed Logan Airport at 8:14. By 8:33, it had reached its assigned cruising altitude of 31,000 feet."

http://www.9-11commission.gov/report/911Report_Ch1.htm

This document states that Flight 175 "departed" at 8:14.

FAA report, Executive Summary, Chronology of a Multiple Hijacking Crisis, September 11, 2001, Sept. 17, 2001 [Referenced Chapter 1, The 9/11 Commission Report, "We Have Some Planes," footnotes 40, 41] (page 1 of 3)

http://www.gwu.edu/~nsarchiv/NSAEBB/NSAEBB165/faa5.pdf

This more detailed FAA document states that Flight 175 began its takeoff roll at 8:14, and that at 8:23, "Flight 175 established radio contact with Boston Air Route Traffic Control Center (ZBW). 'Boston, morning, United one-seventy-five out of one-nine (nineteen thousand feet) for two-three-zero (twenty-three thousand feet).'" The document continues that sometime after 8:23, Flight 175 was instructed to climb to 31,000 feet, and that at 8:40, Flight 175 radioed that it was at 31,000 feet.

FAA report, Summary of Air Traffic Hijack Events: September 11, 2001, Sept. 17, 2001 [Referenced Chapter 1, The 9/11 Commission Report, "We Have Some Planes," footnote 44] (page 12 of 59)

http://www.gwu.edu/~nsarchiv/NSAEBB/NSAEBB165/faa7.pdf

JPEG here - click to enlarge and read or print:

So what does this all mean? Is the BTS database wrong? If not, how could Flight 175 radio that it was at 19,000 feet at 8:23 when it was just taking off? Could Flight 175 have reached 31,000 feet in 17 minutes at a normal rate of ascent? Would Flight 175 have been in the location it was said to be at various times if it in fact took off nine minutes later? If the FAA thought it was speaking to a plane that was at location X, and Flight 175 was not in fact at location X, what does that mean?

[Update: Another reason this time is important has become apparent to me from reading this FAA Report on Aircraft Accident about Flight 11:

http://www.gwu.edu/~nsarchiv/NSAEBB/NSAEBB165/faa6.pdf

At page 3 of 4, the report states that Flight 175 made visual contact with Flight 11 and verified Flight 11's altitude at 8:38 a.m. (1238 universal time). This would not have been possible if Flight 175 left the ground at 8:23 as BTS says, rather than at 8:14, as the FAA and the 9/11 Commission say, because Flight 175 would have been 50 miles or more east of Flight 11's reported flight path.]

I don't know if my questions make sense as my knowledge of air traffic control comes from watching John Cusack and Billy Bob Thornton in "Pushing Tin." But given the war games going on, and the fact that as many as 11 planes were reported missing on 9/11, I have to wonder if the discrepancy in take off times means that the FAA in the documents above was not tracking and talking to Flight 175, but to some other plane or blip.