Thank you, FriedaBlass, for your quick and helpful reply

WineCountryUA, I'd appreciate your second opinion on a few matters, if you wouldn't mind sharing:

1. Do you (like FriedaBlass) also not trust the 30-day grace period?

2. If I call UA 29 days after the ETC expires to book a placeholder flight, then cancel the placeholder flight at least 24 hours thereafter, will the FFC they then issue me expire 12 months from the date I book (effectively giving me a 13-month extension), or 12 months from the date the ETC expires?

3. In your opinion, is it better to (a) use my ETC to book a placeholder flight for 12 months in the future, then change the dates and cities when I know when I want to fly, or (b) book a placeholder flight, wait 24 hours, cancel, then receive an FFC that expires 12 months from the date of booking? As I told Frieda, (a) and (b) appear to accomplish the exact same thing, but perhaps there's an advantage one option has over the other, of which I'm not aware?