I can honestly say that I never noticed loosing my "plug" with any of my 4 pregnancys... I went over 14 days with #1 and was induced. Went over 10 days with #2, induced (was dialated to 2-3 cm for 4 weeks) Went over 10 days with #3 was induced... dialated for weeks also.
I am currently waiting for #4 to arrive... I was due 5 days ago and if it doesn't happen before the 6th will be induced. Already dialated to 3 cm...
As soon as you start dialating your plug is not held in... If you are a fast dialator then you will see the chunk of mucus... If not, it sloughs off and is just flecks here and there.
My MIL swears that once you loose your plug you have the baby with in 72 hours. lol My mom says not so... she would loose hers weeks before labor would start... It depends on you... As for the " could arrive before they are due..." lol depends on you and when your baby is ready...
I am sooooo hopeing I go into labor tonight so I can sleep on my back without feeling light headed, no flipping over 600 times a night, and a slow down on the midnight pee trips... Plus being able to see this child that apparently has as many legs as an octopus and is in the prebirth chuck norris kick boxing class.... :-)
Good luck and each day gets you closer!!!