Bloody show is indeed losing the mucous plug. source
. I'm not clear on exactly what causes the bloody tinge to the mucous; I assume it's from ruptured capillaries, as you said. Where it gets confusing is you can lose your plug without having bloody show (but you can't have bloody show without losing your mucous plug--though you can
just have a little bit of blood from broken capillaries without having actual "bloody show"). Why some women have bloody show and some just have "normal" mucous is anyone's guess; I imagine it to be a feature of your cervix more than anything else.
As to how you can dialate without losing your plug...For starters, it's quite possible to lose pieces
of the plug, esp. if they're not blood-tinged, without noticing. Secondly, we're talking mucous here. It's stretchy. It's perfectly concievable, if you think about it, that the plug could stretch some.
Now, with my second daughter, I had a midwife tell me that labor tends to start within 48 hours of losing your plug...And I guess Linda heard her, 'cause I lost my plug Friday night & went into labor Sunday night. :LOL