It's very frustrating because we can't phsycially see what's going on! ONly rely on the u/s to give us some idea...in terms of LUFS, I believe, and I may be wrong, that the egg does not release, but the follicle "acts" like it did. Sounds like lupron helps with this. I agree with MargieD, that it may take a few cycles to figure out what's going on and if you really have LUFS.
I think in empty follicle, it could go either way (it depends on why it was "empty", which is really a misnomer becaus they are not empty, it's just that for some reason the egg doesn't release...it could be improper medication, faulty egg, or trigger too soon...or maybe even LUFS?? I get confused as to what determines LUFS vs. empty follicle...I think there are other reasons so depending on why you get the empty follicle, the egg might still be released later). At least when I had empty follicle, they said the egg might still release so I did an IUI as a backup as I had only one follicle and they couldn't get the egg out...(if was BFN but that's another story).
If it's the situation where your follicle must be bigger before normal trigger time, I am not sure how they figure that out unless you do IVF because I am not sure how they'd know if the egg was mature, immature, or dead and relate it to the size of the follicle. I know for me, they always triggered me at 18-19, like they did for my first 2 IVFs, and both times I had empty follicle and immature eggs. I had previously done 4 IUIs and no one suspected anything. (and they actually never did an u/s dpo, so they never confirmed if they did release...my suspicion is that they didn't based on my IVF experience).
Keep us posted on how things go!