Obviously, there was work being done...
A Freedom of Information reply from the New York City Department of Buildings reports that copies of city permits for routine or major construction work within World Trade Center building 7 during the years 1999, 2000 and 2001 could not be located. Records for the “ALT 2” category were requested.
“DOB divides construction work into two main categories: New Buildings (NB) and Alterations (ALT). Alterations are further divided into three types—ALT1s, ALT2s and ALT3s—depending upon the scope of work. An ALT1 is a major alteration in which the use or occupancy of an existing property changes. An ALT2 is an alteration in which the use or occupancy of a facility does not change, but includes multiple work types, i.e., plumbing and construction. ALT1s and ALT2s must be filed by a registered architect or licensed engineer."