i didn't know it was originally on the 30th either until i saw it on http://www.sikhnet.com/sikhnet/register.ns...BaisakhiHistory
"On Baisakhi Day, March 30, 1699, hundreds of thousands of people gathered around his divine temporal seat at Anandpur Sahib. The Guru addressed the congregants with a most stirring oration on his divine mission of restoring their faith and preserving the Sikh religion..."