tense choice for one example

Hola George

Here:

"They achieved the objectives for the year" we could use the Indefinido or the Pret. Perfecto:

I'm not sure what translation in Spanish you've seen as there is no link to the lesson/quiz where you've seen this sentence, but this translation could be an option.

So, the use of the indefinido or perfecto are both correct; it depends on the person seeing this as a completed action with a beginning and end (indefinido) or not giving any particular relevance to when this happened, or implying that this is a recent event (perfect). 

The examples that we give in the lesson that you tagged  When to use the perfect tense versus the simple past, are slightly different. They are referring to doing something "this year", connecting it to the present time as we would still be part of "this year"; for example: 

This is referring to something that has happened this year and still connected to today, therefore you see the perfect tense.

In the sentence that you found outside this lesson:

Ellos consiguieron los objetivos del año/anuales.

The words "del año/anuales" are acting here more as an adjective, not as a time marker. So we can use the Indefinido here because what it is saying is that "they achieved the yearly objectives". 

It has a different perspective to the other sentence using "este año". 

I hope this is what you were referring to. As I said, without seeing the actual Spanish sentence it's a bit difficult.

Un saludo

Inma