Well, to get an extreme example, look at Artzi's ancient saber he posted here for discussion
http://www.vikingsword.com/vb/showthread.php?t=4816
I doubt very much any respectable museum would have enough guts and hubris to attempt "restoration" of this artefact.
As to the Jian you showed, I would be very hesitant to ascribe to it much authenticity after heavy restoration. Likely, after 2,000 years it was covered in heavy layer of stable corrosion and removing it to the level of bright and shiny metal likely changed the geometry of the blade .
No wonder, somebody marveled at how thin and rapier-like it was! It likely became a totally different sword.