Continuing the discussion from Shell Design. Need help in making this in software:
No, the file extension has nothing to do with SU versions.
Your working SketchUp Model File has the extension SKP
Your SketchUp Model Backup File has the extension SKB
See these Help articles:
SketchUp Backup Files — SketchUp Help
SketchUp Auto-Save Files — SketchUp Help
NOTE:
Mac OS X users will notice their backup files are named in a different manner … RTM referenced above.
** Updated broken links to docs on June 2, 2017