This representation of the number 20,000 can still be seen today on a Mexican building from the 15th century. It consists of two purses (the symbol for 8000) and ten feathers (the symbol for 400).
Note how the ten feathers are grouped into two lines of five. This takes care of the absence of an auxiliary base to some degree, since it is easier to grasp two groups of five feathers than to count ten feathers in a single line.