You are right. There are "band plans," and then there are "frequency allocations." The "band plans" are suggested, organized and published by the ARRL, and are essentially gentlemen's agreements about where to operate. The "frequency allocations" are mandated by the FCC in Part 97.
CW is allowed anywhere in any band, as long as you operate within the terms of your license privileges. On 6m, CW is legal from 50.0001 to 53.9999 MHz.
For more information in a very understandable format, go to:http://www.arrl.org/FandES/field/regulations/allocate.html#6
73 Steve WB2WIK/6