The tip for all exams is to study the exam topics that is listed on online for each exam. Then evaluate your understanding of them as you study. Cisco and other vendors don't care in the slightest if the Official Study Guide doesn't cover a topic fully (or at all) hell some tracks don't even have OCGs.
That's helpful, thank you, but where do I turn to actually study those topics? In other words, I grant you that it's important to have an authoritative list, and the OSGs may very well not, but where do I go to learn about the topics on the list, in depth?
The thing about the non-R&S tracks is that most of them assume your around CCNP R&S level before you start so they tend to take a "your the network professional, figure it out" kind of stance.
Kevin Wallace has a decent video course that covers CCNA Collab, CBT Nuggets either has one or they are working on it, and INE has the voice stuff done and I think they need to update it to collab if they ever get around to it.
A good place to find some of the topics will be the UC SRND. I can't speak for anyone else, but I found it to be useful.
I would second what \u\flying_scrunt says about using the SRND for UC but with one caveat. Check the exam blueprint for what version that the test is built off of currently. When I took the exams it was a couple of revisions back from what was the latest shipping version. (Maybe written off v8.5 when 10.5 was shipping or something like that.)
For the most part that wouldn't be a problem except for things like capacity or feature/menu questions that may be lower than current versions or implemented differently. I hope that makes sense without violating the NDA by giving a specific question example.