FFO is first flower open on a specific cultivar in a specific year, it's not its first flower to open ever. I'm not familiar with FFE but I would assume that might be used for the first flower ever on a seedling. FFO recurs every year, so the date of FFO for a cultivar will vary from year to year.
DeweyRooter said: I thought FFE was the first flower ever on a plant new to one's garden. Someone can correct me if I'm wrong, but that's the way I've been using it.
You may well be right, I was guessing. It's not a defined term in the AHS Daylily Dictionary like FFO, CMO and EMO. In your interpretation a new plant would have both a FFO and a FFE in its first year.
Yes, FFE means first flower ever of a cultivar to open in a person's garden. I've even seen FFOE, first flower open ever... which means the same thing.
May all your weeds be wildflowers. ~Author Unknown