Reliability of Pre-Ovy Sheds

So how reliable are pre-ovy sheds? I know some of you don't like them and find them horribly unpredictable. I was just curious as to what the data is regarding them.

I'm trying to see if I can estimate when my normal girl will ovy. She's HUGE and gaining weight by the second (not really...but she's gained nearly 200g in 2 weeks...that's also with a poop during that time). She's pounding food and is noticeably larger and appearing rather "lumpy". She's been paired since October. Her most recent shed dates are 1/4/2013, 2/4/2013, and 3/14/2013. I also caught her bowel wrapping before I fed her today and a few days ago I saw her laying slightly inverted (she was laying on her side) and wrapped. I made a thread about it when it happened.

In my experience, there's no such thing, especially since there are no guarantees until ovulation. My girls shed, glow, ovy, shed, lay.

This is interesting, my girl has recently been laying on her side alot, and shed just 2 days ago, been pairing since Nov 1st 2012, so far I palpated nothing, maybe I'm doing it wrong but still waiting... Talk about nail biting experience....