The phrase "notable omissions" refers to important things or people that were left out or not included in a particular list, group, or collection. Full definition
There was one notable omissions from our end of the year list of the best e-readers of 2015. (goodereader.com)
But there's one notable omission in this release of pics, which you can see for yourself below. (slashfilm.com)
There are other notable omissions too so it's either ignorance or an oversight that not every country is represented fairly in the game. (thegamer.com)