How would you know whether an ancient culture had zero?

A few weeks ago I wrote about the number system used in labeling spreadsheet columns. Labels run from A through Z, then AA through AZ, etc. This looks a lot like base 26, but it’s not quite the same. It has no analog of zero. If Z were like zero, Y would be followed by AZ. The Excel labeling system is not base 26, but what’s called bijective base 26. If you found fragments of writing from an ancient culture and inferred that five symbols were used as digits, how could you distinguish base 5 from bijective base 5? Suppose you believe these five symbols were digits ★ ☗ but you don’t know in what order. You just see sequences like and ★★ and believe they’re numbers. If you noticed that numbers often contain , but never appears at the beginning of a number, you might infer that is a zero. But this would take a fairly large sample. If you found only 20 numbers, for example, you could hardly conclude never appears at the beginning of a number just because it doesn’t come at the beginning of…