Dejamos constancia del juego de llaves.

It is a fixed, formal expression meaning to place on record, to state for the record, or to formally note something.

So Dejamos constancia del juego de llaves does not literally mean we leave constancy. The verb dejar often means to leave, but in this expression it works idiomatically:

• dejar constancia de algo = to record / formally note something

This is very common in administrative, legal, and official writing.

Because dejamos can be either:

• present indicative: we leave / we record
• preterite: we left

Out of context, the form is ambiguous. But here the phrase dejar constancia de is a formal written formula, and in this kind of sentence it is normally understood as a present performative: we hereby record or we formally note.

So even though dejamos can sometimes mean we left, that is not the natural reading here.

In formal documents, Spanish often uses first person plural to speak on behalf of the people signing, the institution, or the parties involved.

So dejamos can imply:

• we hereby record
• we, the undersigned, note
• we state for the record

This is very common in reports, inventories, handover documents, contracts, and official statements.

Because Spanish normally leaves out subject pronouns when the verb already makes the subject clear.

• dejamos already tells you the subject is we
• so nosotros dejamos is usually unnecessary

Adding nosotros would only be done for emphasis or contrast.

No. Even though the words look similar, constancia here does not mean English constancy.

In this expression, constancia means something like:

• record
• written note
• evidence
• formal acknowledgement

So in this sentence it is closer to record than to persistence or steadiness.

Because del is the mandatory contraction of de + el.

Here is the structure:

• dejar constancia de algo = to record something
• el juego de llaves = the set of keys

So:

• de + el juego de llaves → del juego de llaves

In standard Spanish, de el normally becomes del.

Yes. In this sentence, juego means set, collection, or matching group, not game.

So:

• juego de llaves = set of keys / key set

Spanish uses juego in this way in several expressions, especially when talking about items that belong together.

Because juego de llaves normally refers to a set containing more than one key.

That is the usual fixed expression for a key set or bunch of keys. Even if the exact number is not important, the plural is natural because the idea is a group of keys, not just one key.

• llave = key
• llaves = keys

Yes, very formal.

Dejamos constancia de... sounds administrative, legal, or documentary. It is the kind of thing you might see in:

• an inventory
• a handover report
• a rental check-in/check-out document
• an official statement

In everyday speech, people would usually say something simpler, depending on the context.

Not usually. It sounds much more like written official Spanish than casual speech.

In ordinary conversation, someone would more likely say something like:

• Anotamos las llaves
• Queda registrado el juego de llaves
• Hacemos constar que se entrega un juego de llaves

The exact alternative depends on the context, but your original sentence has a distinctly formal-document style.

Because the standard expression is dejar constancia de algo, without an article.

So Spanish says:

• dejar constancia de...

not usually:

• dejar la constancia de...

Here constancia functions as part of a fixed phrase, almost like to put on record in English.

Yes. Llave can have other meanings in Spanish, depending on context, such as:

• key
• tap/faucet
• sometimes wrench/spanner in certain expressions

But in juego de llaves, especially in an official inventory or handover context, it clearly means keys.