Tweak - Narrow the rate-row growth claim to the states that actually duplicated.

The changelog entry named three triggers — a period, a space, and a non-Latin
character. Measured against core, only one of the three is right.

WC_Tax::prepare_tax_rate() stores tax_rate_state as strtoupper( sanitize_key() ),
and WC_Tax::get_matched_tax_rates() matches it with `tax_rate_state IN ( %s, '' )`.
So a row is unfindable — and duplicated on every calculation — only when the
stored value is non-empty *and* differs from what the lookup asked for.

A space never diverged: the old str_replace( ' ', '' ) lookup happened to agree
with sanitize_key() there, and only there. A state that collapses to '' outright
never diverged either, because the blank satisfies the second arm of the IN
clause whatever was asked for. What actually duplicated is a state that collapses
*partially*, to a shorter non-empty code: 'N.Y.' -> 'NY', 'ÎF' -> 'F'.

Rewords the entry to key on the mechanism rather than on scripts, and applies the
same correction to readme.txt, which carries the published verbatim copy. The
state_compact() docblock carried the same overbroad claim and gains the boundary.

Author: bartech

changelog.txt

@@ -9,7 +9,7 @@
 * Fix   - Prevent tax calculation from failing when the store address postcode holds more than one comma-separated value.
 * Fix   - Accept lower-case country and state codes from the woocommerce_taxjar_nexus_address filter.
 * Fix   - Fall back to the store address when a custom nexus address is incomplete instead of abandoning the calculation.
-* Fix   - Prevent unbounded growth of WooCommerce tax rate rows when the customer state contains a period, a space, or a non-Latin character.
+* Fix   - Prevent unbounded growth of WooCommerce tax rate rows when the customer state contains a character WooCommerce strips before storing it, such as a period or an accented letter.
 * Fix   - Restore tax rates on the price display, shipping tax and coupon paths for addresses whose state was stored in a normalized form.
 * Tweak - Centralize TaxJar address handling in an internal value object. No change to tax calculation.
 * Tweak - Store tax rate rows against the postcode the rate was quoted for when the address postcode holds more than one comma-separated value.

readme.txt

@@ -79,7 +79,7 @@ This plugin relies on the following external services:
 * Fix   - Prevent tax calculation from failing when the store address postcode holds more than one comma-separated value.
 * Fix   - Accept lower-case country and state codes from the woocommerce_taxjar_nexus_address filter.
 * Fix   - Fall back to the store address when a custom nexus address is incomplete instead of abandoning the calculation.
-* Fix   - Prevent unbounded growth of WooCommerce tax rate rows when the customer state contains a period, a space, or a non-Latin character.
+* Fix   - Prevent unbounded growth of WooCommerce tax rate rows when the customer state contains a character WooCommerce strips before storing it, such as a period or an accented letter.
 * Fix   - Restore tax rates on the price display, shipping tax and coupon paths for addresses whose state was stored in a normalized form.
 * Tweak - Centralize TaxJar address handling in an internal value object. No change to tax calculation.
 * Tweak - Store tax rate rows against the postcode the rate was quoted for when the address postcode holds more than one comma-separated value.

src/Tax/Address.php

@@ -367,6 +367,12 @@ public function state(): string {
 	 * to do) covers `'N Y'` and nothing else: `'N.Y.'`, and any state carrying
 	 * non-ASCII, still diverge.
 	 *
+	 * One boundary to that story: a state `sanitize_key()` empties *outright* (`'ЛЕН'`,
+	 * `'东京'`) was never the duplicating shape, because the blank it stores satisfies
+	 * the `''` arm of that `IN` clause whatever the lookup asked for. The rows that
+	 * could not be found again are the ones that collapse *partially*, to a shorter
+	 * non-empty code — `'ÎF'` stored as `'F'`.
+	 *
 	 * Because core applies the same function on the way in, mirroring it here cannot
 	 * lose information the stored value still has.
 	 *