You may or may not remember, but The AM band until about 10 years ago was a mite smaller. In 1997 it's top end was expanded from 1605 Khz to 1705 Khz.
The FCC issued the first two permits in that band September 26, 1997; Thus granting the applications of KQXI-AM, Arvada, CO and KPHP-AM. Lake Oswego, OR. Strangely both run radio disney these days. FCC Press release here: Link
The stated reason at the time for opening up this virgin forest was to reduce AM band congestion. AM band licensees were encouraged and sometimes prodded into migrating their stations up to that new spectrum. By 2005 only 65 stations made the move. The expanded band has a more FM-like approach based on spacings, omni-directional operation, and uniform 10kW (day), 1kW (night) power limits. No stations are shoe-horned directionally into this portion of the band.
The first station to make the move was KQWB-AM Radio in Fargo, ND., is one of the first AM station to completely switch from the traditional AM band to the expanded band. The station was known to cause significant interference to the 1550 KHz frequency and was a prime candidate for the expanded band. They use the new space well fleshing out their sound with Motorola AM stereo.
Before permits there is always testing. Military station KTRK was one of the first in my area. They conducted test broadcasts at 1670 kHz of the Tactical AM Broadcast Service from a temporary location at Fort Meade, Maryland. The call letters stand for "truck," indicating the station was mobile. That was back in February of 1996. The station began broadcasting around the clock February 5 and received reports from as far away as Colorado. You can actually hear an audio clip here: http://audio.bostonradio.org/19b6b45e-ab92-11d8-9fd3-00904703287b.ogg