You're very welcome!
The LR trial versions definitely aren't limited, other than the 30 day time frame.
The most frequent cause I've seen is the NEF files having been renamed between sending them to you and you returning the XMP files.
When they get the catalog, make sure they understand they need to 'find the missing files' rather than import them afresh.
I'll keep an eye open for your files, just to double check they import correctly here.