My bread went poof. Did it overproof?

Howdy,

Last Thursday I began the pre-ferment for my next batch, and let it ferment in my unheated garage, which at this time of year stays at a pretty constant 50ºF. Yesterday, Friday, after 16 hours the preferment had barely risen, so I gave it some warmth while I got my dough ready with my brand-new digital scale and let it do its autolyse. I kneaded everything together using Bartinet's imagine-it's-your-boss technique (turn upside down, slam, stretch and fold). I ended up with 2.7 kgs of dough, which I shaped into four rounds after 4 hours of fermentation with two folds and stretches in between. By then it was 8pm, and put the molds in the garage figuring they would be ready by early morning for baking (that's about how long it has taken my previous forms to double in size at that temperature). At 11, before going to bed, I took a look at them and they were already doubled, probably because the dough had got up to 70ºF during the previous process. Since I wasn't about to stay up till 2am baking, I put the forms in the fridge, which is set to about 40ºF (that took some serious space management).

This morning the forms hadn't grown any larger, but when I scored the first 2 loaves before sticking them in the oven, they deflated to the point where they looked like giant pitas gorditas. (My forms always deflate somewhat when I score them, but never to that point.) With the oven spring they rised to 2" high, and the one we've eaten already had a great crumb and crust and tasted great, it just didn't have the chubby look I favor.

The other 2 loaves I decided not to score, and the crusts rised to over 4" in the oven, but the crumbs decided not to follow suit, so now I have these fat loaves with an inch of space between the top crust and the crumb, which won't save them from getting devoured.

1. Do forms always deflate somewhat when scored?

2. Do you think that this batch's deflation was due to overproofing?

3. Under the same conditions and timelines, could I have prevented this mishap by reducing the percentage of instant yeast? (I used 0.06%, which I think is the standard for French breads.)

Thanks for your attention and your help!