Only you can tell if the cry is genuine or angry/ frustration hon, they are all different and demonstrate it in the own way. Ruby's angry / frustration cry sound more anygry than upset, she sometimes shouts out of frustration. It's hard to describe but there is a difference.
Re: going in, if Ruby is just raging, angry - the moment UT turns to genuine upset I'm in there. With her tbf it's never very long. If you think your LO would be receptive, you could go in whatever the cry and completely without emotion deal with it.
In terms of classic WI/WO - there's a sticky on the FAQ section of TS that might be of some help
Hena