Did the school change their provider for the background service from Kroll for this year?
In general, a lot of HR won't even comment on specific nature of your employment. Some companies have websites set up that shows "from" and "to" dates of your employment. Other companies refuse to release any info on you due to privacy issues (and potential lawsuits).
When Kroll couldn't verify employment themselves, they usually contact you first and ask you to provide a copy of pay stub, etc. In the past, even though admitted students went through background checks after R1, their bosses did not find out that he/she planned on attending MBA FT (unless they wrote the letters themselves) until the student notified them. Also, a lot of companies have employees doing PT MBA or other programs, so big corporations are used to inquiries like this.