Question re: Quiz

Question

Hola,Re: Se la había comprado. How can one tell when reading or hearing this sentence, - if it was a standalone sentence -  that the “se” means  the plural “les” .    For example if this sentence is entered in Reverso:  “Se la abía comprado.”  they translate it as “ I had bought it for              "him”.  So there’s no way to know from the sentence that it was bought for “plural someones”.  Would this conundrum ever happen in real life, i.e. in converstion or writing, or would it always be clear from the preceding sentence?Thank you for your patience,Nicole

Answer

Hola Nicole,
I imagine you might be referring to this sentence from the quiz:
"La había comprado para sus padres. SE la había comprado. (He had bought it for his parents. He had bought it for them.)
I am not sure why you say it as a standalone sentence. In the quiz the whole text should appear, so this way you can see that it is referring to a "plural" "to them/for them". I highlighted the bits of the sentence where you can see the plural.
"Se" is the same in this case for "to him, to her, to them, so in real life the antecedent is always mentioned, otherwise the listener wouldn't know who it is referring to. However, there might be some confusion in a conversation when we are talking about two people and then you use a "se". See this mini dialogue for example:

*Sí, Marcos y Carlos saben que llegas tarde. Escribí una nota y  se la dejé encima de la mesa. 
-¿A quién escribiste la nota? ¿a Marcos, a Carlos, o a los dos?
*Yes, Marcos y Carlos know that you will be late. I wrote a note and left it for him/them on the table.
-Who did you write the note to? to Marcos, to Carlos, or to both of them?

You can see how the second person may want to clarify who her friend left the note for, as "se" could mean him/them. 
Un saludo
Inma

Answer

I believe I have the same question as Nicole. The highlighted portion of the English text corresponds to the use of the indirect and direct object pronouns in the examples, correct? How can one tell the gender and number of the indirect object pronouns in the examples above? I can only guess that it depends on the context of whatever text precedes which, in these examples, is not shown. Without such context wouldn't it be impossible to determine?