IMHO 20µA for the Whole ESP-12 (ESP8266 + SPI FLASH Memory) powered with 3.3V seems very optimist !!,
OK for about 80µA -100µA @3.3V
Espressif datasheet http://espressif.com/sites/default/files/documentation/0a-esp8266ex_datasheet_en.pdf for EP8266 chip says p20 :
The current 20µA is acquired at the voltage of 2.5V
Looks like A.I forgot SPI Flash current ......and test conditions !