There are 5 mythics I'm currently missing, as shown. I have "show unobtained" unchecked. But it is adding Abynissa, Gard's Avatar, and Plague to my needed summary. It correctly doesn't count Wulfgarok and Pharos-Ra.
Interestingly, if I add a filter of ="0" to the level sort, only Wulfgarok and Pharos-Ra are displayed, which leads me to believe that even though it shows the level for Aby, Gard, and Plague as 0 there is something else in their fields (a hidden character perhaps), which is causing the summary to show wrong too.
To further this, if you do sort in game by amount and toggle show-all on, Wulf and Phar show at the front while Aby, Gard, and Plague show at the end.