Simplest thing is to limit a character to being subject to one Heal spell per combat encounter.
That seems reasonable, Ajax, but to be clear, are you saying that is the rule? Or are you saying the rules are unclear and that is how you would handle it?
The rules as written mean you are only allowed to heal a subject a second time if they take more damage after the first time you healed them
and you can only heal the newer damage not any damage that was "left over" from the first healing spell.
So, let's say that Samurai Sally gets shot and checks off five Physical Condition Monitor boxes. Then Harry Hermetic casts Heal on her and gets three net hits. Samurai Sally now has two Physical Condition Monitor boxes checked off... and she gets shot
again!
Sally is having a bad day, but this time isn't hit as hard, so she only looses two Physical Condition Monitor boxes. Sally checks off two Physical Condition Monitor boxes, for a total of four. Harry Hermetic casts Heal on her, gets crazy lucky with his dice, and gets four net hits!
But Sally is only healed for two boxes... Because injuries can only be affected once by any Heal spell.
That's a pain in the astral to keep track of.
So I say just limit everybody to one Heal spell per scene and call it a day. Generally speaking, most
Shadowrun combat scenes don't last terribly long anyway, so its pretty rare anyone really needs to be healed magically more than once. If they do get really seriously injured, you can just handwave it and say the magician takes X number of hours to do their voodoo during off-screen time.