In 1977, Jeffrey H. Tigay published the article Was There an Integrated Gilgamesh Epic in the Old Babylonian Period?
(Ancient Near Eastern Studies in Memory of Jacob Joel Finkelstein, Connecticut Academy of Arts and Sciences, Memoir 19 (1977): 215-18).
Tigay noted that the assumption that the “canonical” version of the Gilgamesh Epic was based on an Old Babylonian version had never been substantiated.
The Old Babylonian Gilgamesh texts might have been independent, disconnected stories, just like the older Sumerian Gilgamesh stories.
Tigay tries to put forward evidence that the Old Babylonian version existed as an integrated epic.
The Pennsylvania and Yale tablets (Gilg P and Gilg Y, respectively) appear to come from the same edition, which contained at least four tablets:
the first tablet has not survived, the second deals with the advent of Enkidu, and the third with the preparations for the journey to the Cedar Mountain.
This series implies that there was a fourth tablet describing the journey itself. None of the other Old Babylonian clay tablets belong to the same edition.
However, they contain episodes that can be found in the “canonical” version and not in the Old Babylonian one.
The Akkadian fragment unearthed in Boghozköi (Anatolia), which dates to the 14th-13th century covers part of the journey to the Cedar Forest and the episode of the Bull of Heaven.
The Hittite retelling of the epic (fragmentary and in prose), which was also found in Boghozköi, covers events found in tablets I-V and tablets VII-X of the canonical version and presupposes events from tablet VI.
The tablets clearly suggest the existence of an integrated epic in the Hittite empire but do not prove the existence of an integrated Old Babylonian version.
However, there are a number of features in the canonical version that can also be found in the Old Babylonian texts but not the in the Sumerian ones.
The theme that unifies the epic is "Gilgamesh's quest to overcome death in some fashion". A turning point in Gilgamesh's quest is the death of Enkidu, which has this effect on Gilgamesh because Enkidu is not his servant, as in the Sumerian texts, but his friend.
The integrating features related to Enkidu's status and the effect of his death on Gilgamesh were already present in the Old Babylonian fragments.
Gilgamesh's tyranny of Uruk, which motivated the gods to create Enkidu, is also mentioned in the Pennsylvania tablet.
These and several other features are missing in the Sumerian Gilgamesh texts, and they only make sense in the context of an integrated epic.
For Tigay, this confirms the existence of an integrated Old Babylonian Gilgamesh epic.
Walther Sallaberger's book Das Gilgamesch-Epos. Mythos, Werk und Tradition (C. H. Beck, 2008) discusses the Old Babylonian version on pages 69-72.
Sallaberger describes the themes and features that distinguish the Old Babylonian version from the Sumerian Gilgamesh texts and which can also be found in the Standard Babylonian version.
The German Assyriologist does not question the existence of an integrated Old Babylonian Gilgamesh epic.
The paper by Andrew R. George cited by b a (“Shattered tablets and tangled threads: Editing Gilgamesh, then and now”) points out that
[The twelve extant Old Babylonian tablets and fragments] demonstrate that already in the eighteenth century the Babylonian written epic was quite different from the Sumerian poems,
that it was from the start a long poetic narrative bound together by common themes and exhibiting a unified plot.
However, there are differences in wording that suggest that the epic's origin “surely lay in narrative poetry transmitted orally”.
The epic only became more “standardised” in its Standard Babylonian version; this text remained remarkably stable until the last extant manuscript of the epic, which dates from around 130 BC.
What George describes on pages 8-10 of his article is not a comparison of four “versions” of the Standard Babylonian epic, as b a assumes,
but the reconstruction of several lines based on three manuscripts, each of which only provides incomplete lines of the passage in question.
On pages 13-15 he shows how a specific passage evolved over time, and on pages 15-17 he discusses “recensions”, i.e. variations between different manuscripts of the Standard Babylonian epic.
b a's answers seems to interpret George's paper as evidence that there was not even a single Standard Babylonian version,
thereby assuming a concept of sameness of texts that is reasonable for printed text (think Gutenberg, 15th century AD) but which seems anachronistic for literary texts that were copied by hand over the course of many centuries,
and in the case of Gilgamesh, often by apprentice scribes. (In fact, even early printed texts exhibited variation, even within the same print run of, for example, Shakespeare's First Folio.)
Note: b a's answer appears to misinterpret the phrase "Standard Babylonian version" as "standard version".
However, "Standard" is capitalised because it refers to Babylonian (as in "Standard Chinese") and not to "version".
Standard Babylonian refers to a specific literary style used during the Mature and Late periods of Akkadian literature.
This style can be distinguished from the older Hymnic-Epic style. (See Benjamin R. Foster: Before the Muses: An Anthology of Akkadian Literature, CDL Press, 2005, pages 3-4.)
The Standard Babylonian version may be called the “standard version” because that is the version that remained (relatively) stable until the last extant manuscript of the epic.