The way I under stand the BMI system is that when you qualify for a level of Status (say Silver after 16,000 status miles earned), your membership year is reset and begins again from the time of qualification.

You now have a year to earn the next level of status - Gold for a further 38,000 status miles after the Silver qualifying 16,000. You have 12 months to do this. If you qualify within the 12 months, your Status is reviewed to Gold, and your membership year starts from that point. You would have another 12 months from that point to earn another 38,000 miles to maintain your Gold status

If for example you flew another 38,000 in the following week, I guess your membership status is 're-qualified Gold', and your Status miles return to zero (unless it happened in the middle of some qualifying itinerary in which case you could get credit for those miles by mailing BMI DC CS), and your membership year begins again.

I guess the strategy is to time your qualifying Status miles earnings to tip over the 38,000 miles target at around the 12 months point if you want to maximise the length of time of Gold status.