for me, I have increased d/c about this time anyway and the difference between thick d/c and mucus plug for me is jelly aspect. If it's thick and gooey it's d/c, if it's clear/green/yellow/blood tinged or streaked, it's plug. This time when it came out whole it looked like a greenish/whitish jello wine cork, yeah, it was gross and cool at the same time!
I have lost a few bits since and some d/c that looked like it could be cork, but I don't think it was.
Typically a 1st time mom will have her baby within a week of losing the plug (that messed with my head when I went 3 more weeks!) and a subsequent mom will have much more variation in it's loss and many women never even notice losing it. They may lose it in labor or it may just fall into the toilet unnoticed.
I agree that if it was blood tinged (more of an indicator of cervical change-capillaries breaking in the cervix as it opens) I would be more worried.