I have had a go at a Report which identifies the date problems and a Batch Update which aims to fix them.  I think it is Ok having tested  it against some live data which has some of these  issues, but a full test is going to take more  work as it will be necessary to introduce the errors covering the full leap year rules (ie is not a leap year if divides by 100 unless it will divide by 400).  The report also identifies errors with month starts, year start and year end dates. 

JNCC_Prob_NBNDates.xml needs to be copied into your report folder. It will give you a report in System Supplied/Problem Identification which will identify Events, Samples and Determination which have the problem and all show the dates which will be used when the Batch Update is run. Try this first to see if you agree with the errors reported and the proposed solution   

JBCCNBN1_dataCorrection.xml needs to go into the Batch Update folder. It will run from Batch Updates/System Supplied/problem Correction (JNCCNBN_dates_1). Take a backup before running this. Run the report again and the problems should have been resolved.

Please proceed with caution using this.