It's really not complicated. You're confusing the value of your claim with the value of the currency you're being paid in...
- The number of shares assigned to each unsecured creditor was a fixed value equal to the value of their claim against AMR.
- The number of restricted shares set aside for unsecured creditors was a fixed number, or percentage of shares. That's registered with the SEC as part of the perspectus, and was used by outside investors to make their buying decisions after the listing opened. If the number of shares needed to settle the claims works out to be fewer than the number set aside, the company has the right (and obligation) to sell those shares to interested parties who also qualified for the restricted stock
Bottom line... You negotiated to receive a guaranteed payment, and took no risk.
Think of it as being paid in US$ by a company who deals in Euros... when the exchange rate fluctuates, the amount they pay you goes up/down, but you get paid the same regardless.
In this case, the company set aside a certain value in Euros, and the exchange rate is working in their favor that they pay a little less, but now have leftover cash. That's theirs. Had the rate gone the other way, there would be no leftover, and the company might have to pay more to make up the difference.
Had your unions taken the approach to negotiate for an ownership stake on a % basis instead of a $ value, you'd participate in the upswing, but you'd also risk taking a hit if the stock floundered on issue like Facebook did.