JSONSchema representation for "YY-MM-DD"

[DanielBauman88]

The uncefact spec mandates using a jsonschema date for the "YYMMDD" format. It's not listed as one of the untdid2379JsonType types that requires an additional context.

This is consistent with the ccts->edifact mappings recommended here - https://unece.org/DAM/cefact/codesfortrade/CCTS/CCTS-DTCatalogueVersion3p1.pdf
For YYMMDD it declares "Map to semantically equivalent ISO representa-
tion without century truncation"

What I'd like to know is what the recommended approach is for choosing the century for a date that only specifies the decade. Different libraries to different things and it'd be good to make sure we're confirming to the unece instead of some arbitrary library.

EG: Libraries always choose the century based on the current date. However they don't all have the same rollover points depending on the current date. EG: Today some libraries might map centuries from 00-70 to the 20th century and 71-99 to the 19th, other libraries might choose 00-69.

What is the recommendation for how the CC should be created for YYMMDD dates?