iPhoto library backup cannot be added to Photo library because the file format is not supported by Photos

I have successfully imported a much older (circa 2012) era iPhoto library from an external hard drive by dragging and dropping the iPhoto library application icon into the 'Photos' application dashboard icon. However, when I attempt the same method for any more recent (2017) iPhoto libraries, from the same external hard drive, it tells me "These items cannot be added to your Photo library because the file format is not supported by Photos." The more recent backups were created via Timemachine before my previous MacBook crashed. Both the 2012 and 2017 backups were created from the same older MacBook, and same operating systems. How can I access these photos? I'm currently using a 2017 MacBook Pro OS 10.13.1. Photos version 3.0.