Thanks for the sample file, it helped a lot.
When importing dates, they must be in the format of yyyy-mm-dd as stated on the import screen. I formatted one of the Joined date cells in Excel using the Custom format choice, copied the cell, then pasted the "Formatting Only" into the other cells. The dates then imported correctly.
For the Cert Training field, which is a checkbox, the import requirement is case sensitive. Sorry there were no instructions on that case sensitivity. The code will be changed to eliminate that case sensitive requirement, but not for a week or so due to some updates on our side.
So you had the correct data of yes or no, but for importing it needs to be Yes or No. Also (and I'm sure you did this) on the import screen make sure the label at the top of the column for custom fields (like CERT Training) is changed from *ignore* to the proper field name.
Thanks again for your help and for posting here to help others out as well.