Hmmmm...
I think you can simply rationalize based upon the Rules.
Non-Scheduled Fire may only come from an FAO with a line of sight to a target. That target may either be registered before the game ( for later Scheduled Fire ) or a visible unit. All on p26.
Use of Recce communication negates the need for an FAO to have LOS to an enemy unit being targeted by Artillery support on the command phase of the turn in which the Recce successfully communicated. Page 10.
If there is no successful Reece communication in the turn the artillery is ordered...then the FAO must have LOS as usual. The previously targeted unit could not be a target this turn - but could possibly be caught in the fire-zone of Scheduled artillery fire planned before the game starts.
Sound ok?