Weight Loss and Hydration

I seem to be really getting into this bread thing with the biggest problem at the moment of not being able to eat enough and therefore gain practice. I'm at this very moment trying to increase the hydration from my usual 60% to 65% (big deal for me). Now today whilst doing this I had a thought that a few days ago, I was making a round loaf and got to weighting the dough following having worked it and the result was something of a surprise. I started with 500g of bread flour, 300g water, 8g active dried yeast, 20g olive oil, 7g salt and 10g of sugar. This is a total of 845g. In the UK a standard loaf I think is 800g though I've never weighed as I don't buy bread. 

In the above I can appreciate that following being in the oven some weight would be lost. However, the surprise to me, even when working in a kitchen at about 62 degree and with a granite worktop, all mixed by hand, I had lost about 35g in the pre-cook weight. I have considered that some may be due to residue in the bowl. But 35g seems a lot. Also, the bowl was scrapped out well. Is this usual just through working the dough. I will point out that the bowl was wrapped in plastic film whilst the dough was rising. This question comes to mind now as today, I'm letting the dough prove in the oven uncovered on the proving setting with a little water in the oven base.

Now I'm thinking, what am I doing to my hydration levels. As I said, I'm going for 65% as I write and having a practice with the tuck and fold. Having just done this, the result a looking good. The final rise and whether the dough hold its round shape will tell me more. I'm giving it a tuck and fold at every 30 mins on this one. Comments appreciated.