I do not have any stats, just experience.
We thawed a 9-cell that was frozen two years prior on day 3. It reduced down to 7-cell. I am now 11 weeks pregnant.
RE said this FET had a 40% chance of working. It did.
The embryo came from an original batch of embryos that gave us twins.
I really think you just never know.
Sorry about your bfn. Better luck next round!