The (arbitrary?) 9 segment number examples from the Russian Postal Codes that were linked and were questioned as to why the USPS did not adopt them are ambiguous depending on how one chooses to fill out the segments of the numbers. For example 4 may be seen as 9. 8 is slightly less an issue, but amounts to 1 segment away from 0 and 9. If a machine or any and all perfectly rule following humans would be writing and interpreting the zip using 10 different characters mapped to the Arabic numbers, then it would be more optimal to try to maximize the mutual distance between them such as an anti-reflected binary code, which would be an increasingly challenging exercise with more segments that could start at 7.