It's been my experience ( seems to happen a lot lately too) that no matter HOW much fluid you drain from an engine, transmission or rearend, there's ALWAYS more fluid lurking inside, biding it's time waiting for the first chance it gets to pour forth and make it's move on your floor, when you've got your guard down and forget the drip pan.
I wish I'd taken the time and money to put down some kind of coating on my shop floor back when I'd built it. One day I'm gonna pull everything out, clean the floor and do it.