Getting comped has been discussed ad neaseum, along with the challenges. The short answer is that you should be able to show evidence of your current status on another airline and get comped. For more info, do a search.

On your other question - as a Platinum member, you get double base miles. So, if you fly 18,000 miles round trip, you'd get another 18,000 platinum bonus miles deposited in your account. The platinum bonus miles do not count towards elite status.

But, if you fly in paid J (business) class, you will earn an extra 25% bonus miles (which also doesn't count for status), so you'd get an extra 4500 bonus miles per trip.

However, you can also qualify for elite status based on "points." The point requirements are the same as the miles requirements (i.e. 50,000 points for platinum), but they are based on the fare you PAID. 0.5 point per mile in discount economy, 1 point per mile for full Y, 1.25 points per mile for business and 1.5 points per mile for first class. So, if you fly business on an 18,000 mile trip, you'll get 22,500 points, which will help you get status more quickly.

Exchanging earned upgrades for miles will get you more miles, but they won't count towards your status.

Hope this helps.

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