Okay, anyone who hasn't seen @oncebitten360s video on reform types should go watch it now. It's short, concise, and answers every question I've seen in this thread so far.
To paraphrase him, at the end of each reform within a combat you check for two things:
1) Do I have at least the same NUMBER of models in combat as I had before?
2) Have I taken any characters from combat?
Once you've completed all your reforms in a combat, you answer one final question:
1) Does the enemy have the exact same models in combat?
If you can answer "yes" to all of these, congrats, you have legally reformed.
@fjugin Was this answered earlier? I can't remember. Do you check it after each units combat reform or just after all your units have combat reformed?