Alexa Echo only plays songs recently added to my Library?

[trevmation]

Plan

Premium

Country

USA 

Device

Amazon Echo Dot

My Question or Issue

 When I tell my new Alexa to "shuffle songs from my library", it only shuffles songs added within the last year or so to my library. It never plays songs I added a while ago. When I scroll down to the bottom of the shuffle queue and click on the last song (to load more in), none more load. How do I get my Alexa to play all my songs on shuffle? 

P.S. It's not just some weird probability thing with my songs. There are more songs in my library that I added a long time ago rather than more recently. I don't have Prime, if that has any bearing on the situation.