I got different results with 1.6.3 compared to 1.5 using the SAME mp3 files in both, so there is a difference with the recognition method between those versions. This happened on several simple pop songs. 1.6.3 seems to show some basic minor chords as major, while 1.5 correctly displays them as minor. That's the only difference I found. It's hard to test more because 1.5 can not be used anymore.
But all in all, Riffstation has been great. I bought it for $29 in 2013. For some reason I never got any emails about closing the servers a year ago and I've been able to use version 1.5 until just a few days ago when it started asking for activation renewal.