Since I'm the one who asked Wolfe the question on the People Website interview (http://pathfinder.com/people/interactive/wolfetrans.html) I'll state that I'm certain he is giving two seperate answers to two seperate questions.
first, I ask him how long between the New sun series and our own period, and then I ask how long between Typhon and Severian. He answers "That is never specifed in the books" and "My offhand guess is between 1000 and 2000 years".
Chatroom conversations being what they are, and that it is the only way to assume he tried to answer both questions, I believe he is only making an offhand guess at the T-S duration.
Or maybe he's being deliberatly enigmatic :-)
"I am an impure thinker. I am hurt, swayed, shaken, | paul + | + elated, disillusioned, shocked, comforted, and I | --|-- have to transmit my mental experiences lest I die." | + | +
-- Eugen Rosenstock-Huessy | pduggan at world.std.com