DOB not known in credible sources 
A fellow contributor at werelate.org offers that:

He was not born on the 9th.  When he was actually born is unknown. What is known is that he was baptized on the 16th.  If you look at the bottom of the page, the 'source' used for this is actually a random GEDCOM site with all unsourced information - they have a hilariously long Webster line that is complete fantasy.

And although I havent gotten around to it, I believe his 'death' date may actually be a burial date, but I need to confirm that.

Our page at werelate: http://www.werelate.org/wiki/Person:John_Webster_%283%29