This isn't called out in TR-35, but before ICU even looks at CLDR data,
it adds a hard-coded set of default patterns to each locale's calendar.
It has done this since 2006 when its DateTimeFormat feature was first
created. Several test262 tests depend on this, which under ECMA-402,
falls into "implementation defined" behavior. For compatibility, we
can do the same in LibUnicode.
