That Library no longer exists under YOURUSERNAME. I set up a Test account and a YOURUSERNAME this Mac a few months ago, prior to the Steam update, and Downloaded most of my models/subassemblies to this platform. The platform is iMac 27-inch late 2013,
3.2 GHz Intel Core i5 with 16 GB DDR3 memory. If one travels back in Apple's OS X file structures by a couple years, those Libraries you mention may exist? Thx for feedback. My new iPad Pro (A9X processor) works just fine with the pre-Steam SimplePlanes. So, some good news! @AndrewGarrison

@Stingray That is weird, if the game is working at all for you now, you should have this folder: Macintosh HD ▸ Users ▸ YOURUSERNAME ▸ Library ▸ Application Support ▸ Jundroo

Completed search of entire file structure. No Subassemblies or AircraftDesign folders. More pertinent is that ".xml" files are not viewable (a year ago they used to be within the iTunes folder). I would to need to pull apart the binary 268.2 MB SimplePlanes.app file to find out where all the downloads wind up. Only the OSX 10.11.2 System has permissions of both read & write on this app. @AndrewGarrison

@Stingray Have you tried searching your system for a Subassemblies folder or a Subassemblies.xml file or an AircraftDesigns folder? Maybe it will find where the old files are at. If you can find them, then we can move them to the new location.

So says SP - but the old device in question is made by Amazon. No Google files tricks allowed on it, very similar ti iOS. Identical limitations - no sub-file visibility or ability to backup files for SP. An old device, gonna dump it. Just got an iPad Pro with 2.26 GHz CPU. Gotta re-build some files from SP on it, MAYBE. Not too sure how much I trust SP/Jundroo releases in the future. [After six unlisted file uploads Jundroo said I'd exceeded my upload limit. But, they were unlisted....so?] @Delphinus

Understood. Home devices are not PC or Android devices, am limited to Apple software Idiosyncrasies. Jundroo and @AndrewGarrison clearly do not go for the Apple User market, OK. that's life. Move on to new software, for me... SP. maybe, maybe not,...@Delphinus

See my note above to @Delphinus, @TheLatentImage, @Nickasaurus

Thank you, I gotta post all I've build from my old iPad, since the STEAM upgrade trashed all men desktop models; unless I put it on SimplePlanes, including subassemblies, I will never be able to use my build library. Having multiple emails with AndrewGarrison about that. @Delphinus

Thank you, @Nickasaurus

Thank you, @TheLatentImage