Glenn Hauser found this link that may shed some light on the 590/1020/1610 test situation.
This appears to be a 2005 Special Temporary Authority for BAE Systems to operate test transmitters on these frequencies. Some explanation excerpted from the FCC document:
Please explain in the area below why an STA is necessary:
Required to complete full scale transmitter and associated equipment testing.
Please explain the purpose of operation:
Company is a govt contractor which is developing mobile broadcasting units which can be deployed worldwide in order to satisfy customers immediate military requirements. Broadcast operation encompasses use of AM band frequencies which are necessary to simulate overseas operating parameters.
Bowling Green Virginia North 38 7 59 West 77 19 49
(a) Overall height above ground to tip of antenna in meters: 50.00
585.00000000-595.00000000 kHz FX 10.000000 kW 9.750000 kW
1015.00000000-1025.00000000 kHz FX 10.000000 kW 9.750000 kW
1595.00000000-1605.00000000 kHz FX 10.000000 kW 9.750000 kW
This STA, however, expired in November 2005. (and note that it specified 1600KHz instead of 1610) It sure does look a lot like what we've been hearing though.
This is an Office of Engineering & Technology STA. STAs for operation in the broadcast bands are now handled by the Media Bureau; however, this is a relatively recent change. (I believe OET STAs were legal for broadcast frequencies in 2005) This may be why there has been no information from the Media Bureau: it's quite possible they aren't aware of this STA!