The last stretch of the Slavonic alphabet is where the two scripts were doing their most original work, and it is also where the modern lists agree least. Everything from the affricates onward records a sound Greek did not have, so nothing could be inherited and every sign had to be decided. The reduced vowels, this vowel, the letter for yat, the glide sequences and the nasal vowels are all in that stretch.
The consequence is that the tail of the alphabet is the part where authorities differ over the inventory, over the order and over whether particular signs are letters or compounds. That is not carelessness in the sources. It reflects a real situation in the manuscripts, which were produced across several centuries in several regions by traditions that had diverged, and which do not present one alphabet to be catalogued.
The atlas lists the letters as the Unicode Standard arranges them and says where the arrangement is a choice among attested possibilities rather than a fact. That is the only honest way to present a repertoire assembled from a tradition that never settled on one. Where a specific question can be stated, such as what a particular sign wrote or whether a name ever carried a sense, it is recorded as an open question so that someone can take it further.