Option 1!
You are now Silver for a period of 12+3 months starting Sept 18.

Less than 100 XP in the first 12 months, and you lose your status after the 15 month period (there are three months 'grace period' if you don't requalify).

Reach 100 XP anytime in the 12 first months (without going to 180) and you'll keep Silver for another 12+3 months (until Sept 20, +3 if you don't requalify).

Reach 180 XP, and you are converted to Gold immediately. This starts a new 12+3 period, for instance your new qualification period starts in June 19 (the September date doesn't matter anymore). Then you have a year to reach 180 again.

See some examples here.
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