HS Codes. Why only 6 digits??? Help Needed.

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HS Codes. Why only 6 digits???

We now require 8 to ship from the UK to Europe.
10 digits to ship to other destinations worldwide.
We fix this by manually changing the codes of each product in each parcel when we enter details with the courier.

Shopify limits you to 6 digits in the HS Code field.

Why? (As its such a simple thing, any coder in the background could fix this is seconds). What is the logic behind limiting it to SIX. Rather than conforming to applied international standards.