Most people are working on builds where debug information was either inadvertently or sometimes intentionally included (e.g. for beta releases sometimes debug builds with debug info would ship for sake of making things easier.) These builds usually don't have all of the normal release optimizations on. That makes it much more likely to get a match.

I haven't tried this, but I also suspect that once you have a lot of code fully matching, it might make it possible to ratchet your way up further into builds that you don't have debug information for, that may have more aggressive compilation options. I am not sure if you would manage to get /LTCG builds fully matching even with this advantage, but it's going to be the best shot at it. You're possibly 90% of the way there already.