Thanks for describing your B&W processing steps.
Oh, I’ve just seen you solved this (as reported in the post above mine). Sorry, I guess I was in write-only mode. 
Anyway:
I’ve made an experiment:
- applied multiple instances of exposure
- left the original instance in its normal position
- moved the top instance near the top
- moved the mid instance to be around the middle
- saved this as a style, including some other modules + the module order module:
Left-hand-side: the style creation window; right-hand-side: the list of active modules in the pipeline.
Then, from the lighttable, I applied this to another image in append mode. The resulting list of active modules is:
So, exposure / top is above filmic rgb, exposure / mid is between is between filmic rgb and color calibration; exposure / scene-referred default is at its usual position.