Faltaba, de ahí que rellenara el parte de irregularidad de equipaje.

De ahí que is a linking expression meaning hence, which is why, therefore, or that is why.

In this sentence, it connects the first idea to the consequence:

• Faltaba = something was missing
• de ahí que rellenara... = which is why someone filled out the baggage irregularity report

A key point: de ahí que is normally followed by the subjunctive.

Because de ahí que triggers the subjunctive.

Spanish uses the subjunctive after certain expressions that present a result, consequence, evaluation, or interpretation rather than just a plain factual sequence. De ahí que is one of those expressions.

So:

• de ahí que rellenara... = hence / which is why ... filled out...

Even though the action really happened, Spanish still uses the subjunctive after this expression.

Because after de ahí que, Spanish does not use the normal past indicative form such as rellenó.

Compare:

• Rellenó el parte. = He/She filled out the report.
  
  • plain statement of fact, indicative
• De ahí que rellenara el parte. = Hence / that is why he/she filled out the report.
  
  • after de ahí que, subjunctive

So the choice is not mainly about whether the action happened; it is about the grammar required by de ahí que.

Because the sentence is talking about a past situation:

• Faltaba = was missing
• therefore the following verb is also framed in the past: rellenara

This is a common sequence in Spanish:

• past context → imperfect subjunctive

If the whole sentence were in a present-time context, you would more likely get the present subjunctive:

• Falta, de ahí que rellene el parte.
  = It is missing, hence he/she fills out / should fill out the report.

So rellenara fits the past narrative.

Faltaba comes from faltar, which can mean to be missing, to be absent, or not to be there.

Here it most likely means:

• it was missing
• something was missing

The imperfect is used because it describes the situation as background information in the past, rather than as a single completed event.

Compare:

• Faltaba una maleta. = A suitcase was missing.
  
  • description/state in the past
• Faltó una maleta. = A suitcase went missing / was missing at a specific moment
  
  • more event-like, more bounded

In this sentence, faltaba sets up the situation that led to the report being filled out.

The subject is not stated explicitly, so it has to be understood from context.

• Faltaba could refer to:

  • el equipaje / una maleta / una pieza
  • in English: the luggage was missing or a bag was missing

• rellenara could mean:

  • I filled out
  • he filled out
  • she filled out
  • you (formal) filled out

Spanish often leaves the subject out when it is already clear from context.

So by itself, the sentence does not tell you exactly who filled out the report or exactly what was missing.

Yes. In Spain, rellenar is very commonly used for filling in / filling out a form.

So:

• rellenar un formulario
• rellenar un parte

Other possible verbs are:

• cumplimentar = to complete/fill out
  
  • more formal, very common in administrative language in Spain
• llenar = to fill
  
  • more general, often physical filling rather than forms, though it can sometimes be used too

For Spain Spanish, rellenar sounds very natural here.

Here parte means report or official form/report.

It is a very common administrative word in Spanish. Depending on context, parte can mean things like:

• a report
• a notice
• a record
• an official form

In this sentence, el parte de irregularidad de equipaje is the official report used when luggage is missing, delayed, damaged, etc.

So parte here is not part in the English sense.

It is a fixed travel/airline expression meaning something like:

• baggage irregularity report
• luggage incident report

This is the form used when there is some problem with baggage, for example:

• it is missing
• it is delayed
• it is damaged
• it has not arrived correctly

So the phrase is technical/administrative language, especially in airports or airline contexts.

Because de equipaje works here as part of a noun phrase meaning relating to baggage.

Spanish often uses de + noun without an article in set administrative or technical expressions:

• centro de salud
• tarjeta de crédito
• reclamación de equipaje
• parte de irregularidad de equipaje

Adding an article, like del equipaje, would make it sound more specific: of the baggage. But here the phrase names a type of report in general, so de equipaje is natural.

It is grammatically understandable, but it does feel context-dependent because both the missing thing and the person who filled out the report are omitted.

Spanish allows that very easily, especially when the surrounding context already makes it clear.

For example, in a longer passage, this could follow something like:

• Una maleta no apareció en la cinta. Faltaba, de ahí que rellenara el parte de irregularidad de equipaje.

Without context, the sentence is still possible, but it leaves some details implicit.

Literally, it is something like:

• from there that

But that literal translation is not how it works in natural English. You should usually understand it as:

• hence
• therefore
• that is why
• which is why

So it is better to learn de ahí que as a single expression rather than word by word.

Yes, de ahí que + subjunctive is somewhat formal or written-style Spanish.

You will see it often in:

• news reports
• formal narration
• essays
• official or administrative contexts

In more everyday speech, people might express the same idea more simply, for example:

• Como faltaba, rellenó el parte.
• Como no estaba, tuvo que rellenar el parte.
• Por eso rellenó el parte.

But the original sentence is perfectly correct and natural, especially in more formal writing.