The firms, which focus on active management, are seeking flexibility to lower fund fees.
American Funds and American Century saw the largest percentage growth last year among prominent TDF providers.
Stepping back to see the forest for the trees.
During 2016, fees hit record lows, assets reached a new all-time high, and asset-allocation techniques improved.
Big contrast with gloomy forecasts from BlackRock, State Street Global Advisers and TIAA.
These mutual funds lost the least in the bear market.