Don’t forget that the previous record was set in 1964, which was a leap year. Therefore May 20th that year was one day later in the year than it is this year, on account of being after the extra Feb 29th. Tomorrow we celebrate.Record gets broken if it's still up tomorrow.
The city (the people running the ice classic up in Alaska) have declared it is a record late breakup.
If you measure from the solar year (days-minutes-hours after the spring equinox, for example) it is also a record late ice breakup.