Hi Thomas,
Thanks for using Syncfusion products.
We have created a sample to achieve your requirement of adding past days to BlackOutDates collection. In the attached sample , we have added nearly 110 days from date of Dec 12, 2012 to BlackOutDates collection.
Please let us know if you have any queries.
Regards,
Swasthika Lakshmi I
CalendarCellTemplateSample_cf67e4d5.zip