Metadata is a complicated topic. The EXIF button in Nitro invokes ExifTool which parses a different (larger) set of metadata from the libraries built into macOS, which is what Nitro uses for general display and also for export.
When exporting, the app creates a new file, so it needs to manually insert metadata for each key that it knows about. The list that Nitro uses is based on what macOS is able to read. If it’s a key that macOS doesn’t know about, then Nitro will not copy it over (because there is no way to do that). On the hand, there may be keys that macOS reads that Nitro doesn’t support, but that would be easy to add.
Please email me separately (at support@gentlemencoders.com) with the keys that you have set (and also a sample file) – I will see if these are ones that Nitro can insert into the exported file.
