You will sometimes come across topics here and there that seem totally random and out of left field - don't let it overwhelm you. Just focus on learning those facts as they come up and move on. Cliff's covers enough information to form a pretty solid foundation - know that resource well and you will be covered for most of the DAT. The additional details from other resources will be helpful for achieving a very high score, but they're not an absolute necessity to do well enough on the DAT.
I'd try to keep a document with a list of facts for whenever you come across new material, that way you can track these extra details and memorize them at your convenience. Personally, I worked new content I came across into my notes for memorization purposes so if you're taking your own notes then just integrate that material directly.
Biology is a huge subject and truly knowing all of it can feel impossible. Doing well on the DAT's biology section is all about focusing on high yield material first and then memorizing whatever else you can. You'll never really cover all of it, but you don't need to.
