Learn English – Past tense: “happen to have” or “happened to have”

There is a valid literary technique that will subtly shift from past to present but it is much safer to pick one tense and stick with it.

An example of this device, which I copied from About.com's page on the subject:

Off the road there was what appeared to be a reviewing stand, and I sat there for a few moments, taking in the museum and the cold blue Sunday sky, taking stock, what to do, what to do next, I'd really hate to cancel dinner tonight . . . I'm breathing normally now, it's OK A-OK, I won't even tell my wife, nor Tim, especially not Tim, I feel fit as a fiddle now.

The page linked above has a handful of various thoughts and examples on the subject. It does explicitly note that we often do this sort of thing during informal speech:

What is an example of an unmotivated shift in tense in writing? One example is starting a story in past tense and suddenly shifting into present tense:

Last week I was walking along a street when this man walks up to me and says...

We do this in speech all the time, but in formal writing it's considered to be an error.

(Edward L. Smith and Stephen A. Bernhardt, Writing At Work: Professional Writing Skills for People on the Job. NTC Publishing, 1997)

It is idiomatic, a the similar expression “murder will out” is from Chaucer (14th c.). The sense appears to be from “out” used as a verb here meaning:

Out:

sense of "disclose to public view, reveal, make known" has been present since mid-14c.

(Etymonline)

Truth will out:

is from Shakespeare's The Merchant of Venice, 1596:

LAUNCELOT: Nay, indeed, if you had your eyes, you might fail of the knowing me: it is a wise father that knows his own child. Well, old man, I will tell you news of your son: give me your blessing: truth will come to light; murder cannot be hid long; a man's son may, but at the length truth will out.

(Phrase Finder)

The phrase "truth will out", or "truth will become public", appears as early as William Shakespeare's works, in particular, the Merchant of Venice. It may have been an entirely new concept of Shakespeare's, as he sees the need to explain its meaning as analogous to murder will out.

(Wiktionary)

From Chaucer, "Nun's Priest's Tale," c.1386:

Mordre wol out that se we day by day.

(Etymonline)