There are 30 cards in the game (to this point, I'm not a playtester but I have everything that is out).
Of those 30:
12 are redirection, they do not say instead, but the instructions clearly state what to do with the damage.
8 deal with increasing/decreasing or preventing damage, and again the instructions are clear as to what to do with the damage.
4 have instead written on the card
1 are Ambuscade's traps, they share the same wording and it is clear since they tell what to do with the trap, they don't need an instead.
3 have no instead, and the triggered effect doesn't deal directly with the cause but have clearly worded instructions (Kismet's Inconcievable Obstruction and Lady Luck, La Capitan's split across time side) that do deal with the initial trigger.
The two remaining are Police Backup and Jack Handle.
The four with Instead on the card are Null-Point, No Executions, Unforgiving Wasteland and Spite's Drug Wracked Monstrosity side. They all deal with a triggered effect that doesn't effect the initial trigger, except that they do say instead, letting us know that the initial trigger doesn't happen.
Jack Handle to me is a mistake of wording stemming from it being in essence a redirection of damage. All redirections use the word would, but they all use the word redirect. Jack Handle doesn't, which is confusing and makes it need an instead which it also didn't get.
While this doesn't give any smoking gun style evidence, it gives us several examples that >G has written of cards that have trigger effects that don't effect the initial trigger, but have wording added to make sure it does, sometimes instead, sometimes just with giving clear instructions.