Customer Activity Statistics for This Year are showing dates from really old years, not the current fiscal year.
In the Customer record, on the Activity tab, the four top lines are for 'Highest Balance This Year / Last Year' and 'Largest Invoice This Year / Last Year'. These are called Activity Statistics. They are not date-sensitive. They are stored in only two buckets - one for this year, and one for last year.
When the AR Year End process / Clear Activity Statistics (under AR Periodic Processing) is run, the 'last year' figures are removed, and the 'this year' figures are moved into the bucket for 'last year'. All transactions entered after the year end are then classified as 'this year' until the year end process is run again. Therefore, the reason for the old year value in the 'This Year' statistic field is that the Year End process has not been run. It is not a mandatory procedure, so this is a common issue.
For detailed information on running AR Year End, see AR Year End