All the commentors cracking jokes are ignorant of what creates these issues: 1) B-2s were made in small numbers decades ago. A lot of the machine tooling is likely long recycled. 2) The plans may have been lost or misfiled. 3) Anyone with experience making these retired years ago. 4) Having plans and having practical knowledge are not the same, particularly for aircraft. This is why China is 20 years behind us in jet engine technology - even with stolen plans and engines to reverse engineer, tempering different areas of a part to the precise degree required is *very* difficult. It'd be akin to handing a bread baker a list of cake ingredients and a finished cake and wondering why their reverse engineered cake always comes out tough. How are they supposed to know that kneading the dough too much makes it too tough and breadlike?