Add Spanish month names (Mexican-branch letters) to config.MONTHS and let
the month-first matcher accept a hyphen (not just a dot) before the year, so
"Mayo 18-1929"/"Junio 7-904" parse without manual overrides. Also bound
4-digit years to 1700-2100 so gross typos ("23-9003") stay in review instead
of producing a bogus year. Cuts unknown-date rate 9.2% -> 7.9%.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>