I'd like to start off with the familiar Angelic Protector + Common Bond scenario.

The official ruling is that Angelic Protector will only trigger once. The logic, insofar as I can tell, is essentially based on grammar, in that it went from ‘not the target’ to ‘now the target’, and that transition only happens once.

I don't know I would be entirely satisfied with that, since if we're using English to determine the meaning of it, ‘the target’ at least implicitly requires that it has no other targets - as far as English usage goes. However this explanation has one further - and more explicit - contradiction within the rules.

The entire basis of the above argument is that an object can only become the target once for a single spell, but when checking whether Deflection can change the target of Common Bond, we get the resounding ‘it cannot, because it has multiple targets. Okay, I’m with you there… But how do we determine this within the rules?

114.8a An object that looks for a “ with a single target” checks the number of times any objects, players, or zones became the target of that spell or ability when it was put on the stack, not the number of its targets that are currently legal. If the same object, player, or zone became a target more than once, each of those instances is counted separately.

So Deflection checks Common Bond, and sees that Angelic Protector became a target of the spell more than once when it was put on the stack, thus it cannot target it… But if this is true, then Angelic Protector should trigger twice.

Conversely, if we reverse engineer the scenario, and start with Angelic Protector only becoming the target once, then 114.8a should only see it being the target once, thus making Deflection able to target Common Bond.

The only potential difference that I can find, is the difference between using ‘becomes a target’ vs ‘becomes the target’ - which is such a finicky difference that I can't imagine this being an intentionally functional difference. It's possible 114.8a could be resolved by switching it from ‘became a target’ to something like ‘was chosen as a target’ - as the latter has no connotations to other rules (as far as I know).

I've mulled over these scenarios for a while, and have yet to come up with a satisfactory answer on my own or in discussions with others. The next step was to post here and hope for a resolution that clarifies things for me.