Does a tube need the break-in hours?

Most probably not, but not sure why :) 
Does anybody know a good substitution for 12AT7WA tubes? I have bought 8 of them about 10
years ago for Manley Stingray. Now, when I need a replacement, none of them are good
(ones are labeled by Manley others are Philipps). 
(An almost 20 years old Stingrey remains in a good shape.) 
I have found and mfg state 100 hours to fully runin . The new metals need to season or settle in as in any metals they sound a bit bright the first 50 hours or so. Power tubes get hotter faster 
and tend to settle down quicker. Some specialty brands say 200 hours I think 100 hours is pretty safe bet.
12AT7 tubes can be called different things, but I am not aware of any substitutes.  For example, 6201 is US mil-spec AT and ECC81 is euro designation.  .

I have a bunch of US ATs and a fair number of Amperex/Philips/Valvo.

You might want to post a wanted ad with the specifics of what you are looking for.  The admins don't want us dealing direct.  I would be happy to post a listing if you let me know what you want.
Uncle Kevvy from Upscale told me the 12au7 and 12ax7 tubes which were NOS would take around 50 hours to break in.