"To" is a preposition that can be used to say many things. You can use it to indicate:
A goal [As in your question]
A direction of movement
A place of arrival.
So, your question:
"Can someone help me [with this thing, now]?"
Yes they can...
"Can I get someone to help me [tomorrow]?"
Yes you can... TO is indicating a goal you wish to achieve - ...
I've never heard your rule, and I don't think it's very helpful as it stands.
One use of could is to make polite requests, eg
Could you bring my bag up for me?
The answer is most often not can or could but will:
Yes, I will!.
No, I won't, because I'm not going that way.
Sometimes the answer is can, usually meaning that the person is ...
1B is incorrect "I'm sure they will have been looking for those bank robbers"--makes no sense. "I'm sure they will have found those bank robbers by morning. By tomorrow morning, they will have been looking for those robbers for over 20 hours." makes sense. You need a reference of a stopping point in the future.
You can use 'every' or 'no' in these ways to express a limit
Every X must/shall be less than Y.
No X shall be greater than Y.
Every suitcase must/shall weigh 15 kilos or less.
No suitcase shall weigh more than 15 kilos.
The short answer to OP's why did 'I' use 'could have pp' instead of just 'could return'? is that OP isn't a native speaker (so he made the wrong choice of verb form).
The construction could have [verbed] usually references something that might have happened in the past. It doesn't work in OP's context (where "then" refers to the future time "later today, ...