this is a waaaaaaaaaaaaaaaaaaay delayed comment...

But with regards to "the signature objects on each side (javascript versus java) would return different r and s combinations, although I later discovered that both were still validating correctly! If anyone has more insight into why this is, please feel free to share in the comments..."

It's because ECDSA signatures are generated using a secret number k which is NEVER the same (leading to different r and s). See http://nlitsme.github.io/posts/2014-06-19-ecdsa-explanation/