Give 10 bones and ask to arrange them by any criteria. So you arranged them into a sequence.
Give the 11th bone, ask to insert it into the sequence.
You can always do that.
That is your evolution theory: a game of classification.
In the first place, taxonomy is not about a linear sequence. It is about grouping things into categories.
Still your analogy holds this far. If one is arranging ten bones into e.g. three categories, one can always add an 11th.
But will you get the same groupings if you change your criteria?
For example, if you are grouping the bones by length you may get the sets A=1, 5 6; B=2, 3, 8, 10 and C= 4, 7, 9
But if you are grouping the bones by colour you may get the sets A=1, 3, 8; B=4, 6, 9, 10 and C=2, 5, 7
What makes the classification of living things special is that they fall into a nested hierarchy even when you change the criteria. In fact they fall into the
same nested hierarchy even when you change the criteria.
Can you still add the 11th bone? Depends. If you are dealing with a small clade, and the 11th bone does not have the characteristics of the clade, it can only be added as an outgroup: not part of the set of 10 bones you have been dealing with.