In answer:
1: downgrade failure> don't know but i succesly downgraded to 3.55 Rogero v2 "i have recovery mode ok"
2: ros0 or ros1 empty > "No" i'm verified with flowrebuider
3: flash corrupt > "No" i changed the component
4: general hardware failure > last soluce perhaps but i'm not sure why question one. and for that i want it's possible to downgrade in 2.76 with QA flag !