Bagel internal temperature problems

I'm on a mission to learn to bake New York style bagels at home.  I'm not a bread baker so this has been a great learning experience so far.  I've tried to be methodical in learning and I'm getting close to my goal after many failed attempts and corrective actions. Once I discovered that I was over-proofing my bagels, my recent results have been much improved. 

My current problem is getting the internal temperature of my bagels close to 200F.  I test the temperature with a probe thermometer right after pulling the bagels out of the oven and I seem to be stuck at 170 to 180F.  The color is great and the bagels have a good crunch and "crumb".  I suspect however that they are under baked. My recipe calls for an oven temp of 425F for 15 minutes, yet, I've baked them as high as 450 for 20 minutes with the results seemingly stuck at an internal temperature of 170F to 180F.

I'm hopeful that you more experienced bakers can help me to pin down the factors that maybe involved in bake times and temperatures.   I'll include my recipe,  process and some pics in the post below.  

Note: I still may be over proofing the bagels somewhat.  I've reduced the proof time once already, but I still think they may be deflating a bit after boiling. 

Recipe:

Sponge:

            Warm Water                          190 grams  (room temp to encourage yeast growth)

            Bread Flour                          125 grams

            Active Dry Yeast            1.5 grams (½ tsp)

Combine in mixer bowl cover with plastic wrap and let rise for 2 to 3 hours until it looks foamy

Dough

            Bread Flour                        200 grams

            Sugar                                    12.5 grams

            Diastatic Malt                        12.5 grams

            Salt                                    5 grams

Replace the mixer bowl with the sponge back on the mixer and change to the dough hook. Using a slow speed, slowly add the dry ingredients.  Let hook knead the dough for 20 minutes.

After dough is fully kneaded cover and refrigerate for 20 minutes.

Form into Balls and return to the fridge for 10 minutes

Form into bagels and let proof for 10 minutes (float test)

Refrigerate overnight

Next Day Set up  - make sure rack is at center of oven.  Let preheat to 500 while heating water bath

Bath:

Add 1tsp soda, 1tsp molasses to water to boil

Boil 1 minute per side

Seed

Bake

Reduce oven to 450 & Bake for 8 minutes then turn pan and bake for 12 more minutes.