I am struggling to figure out how to translate the following:

• “for the first time this year, X happened” (i.e., X has happened in the past, but this is the first time in this particular year that it has occurred)
  
• “this year, for the first time, X happened” (i.e. X has never happened before, it’s the first occurrence, and this first occurrence is in the current year”

Can anyone assist in a good way of expressing these meanings in Esperanto? Dankon!!

Unuafoje X okazis ĉi-jare. = X okazis ĉi-jare kaj ne estis antaŭe.
Unuafoje en ĉi tiu jaro X okazis.

Ĉi-jare, por la unua fojo, tute ne neĝis en Novembro

Ĉi-jare ni devis atendi ĝis Aprilo por vidi pluvon.

Alivorte, depende de X, vi eble facile trovus rimedon por distingi. per restrukturigo de la frazo.

Cetere, mi min demandas ĉu la distingo (dependa de kiam okazis por la unua fojo X) estas tiel klara en la angla kiel vi supozas.

Elparolu jenajn du frazojn kaj petu ĉe anglalingvano kio estas la implico.

For the first time this year, it didn't snow in November
This year, for the first time, it didn't snow in November.

In a normal conversation I surely would mix the expressions (I'm not a native speaker of English), and choose an interpretation, that suits my experience. In this case: the first snow usually falls already in November, but it doesn't stay; permanent snow often falls as late as in January. So the expression "must" mean, that the first snow didn't fall in November this year and that was exceptional.

I made a short inquiry among my friends about how they understand the sentences. What very likely invalidates the inquiry, is that I translated the sentences into my native language, Finnish. I used different grammatical cases to express the difference as that is the natural way to express it. Word order change would have only changed the emphasis, not the meaning. The case-based approach uses time expressions (for "for the first time"), that use accusative resp. partitive, or in layman's terms whole object and partial object.

The accusative-based expression corresponds to the perfect aspect in the Slavic languages, i.e. the observation framework is limited or closed, this year, so the sentence must mean, that the snowing was the first time in this particular year.

The partitive-based expression corresponds to the imperfect aspect in the Slavic languages, i.e. the observation framework is not limited or closed, so the sentence must mean, that the snowing in November was the first time ever.

To put this back to the original question I agree with Sudanglo. You must restructure and use additional words to make clear, which message you want to transmit, simple word order change is not sufficient.

More generally speaking English is full of idioms, that one should not try to translate word for word into E-o. A better way is to think out, what those idioms actually mean and express that meaning.