I have recently been in e-mail conversation with Philip Engmann, a Ph.D. student in Ghana trying to sort out his own OTTC methods, and our discussions have raised a few points worth noting for further consideration. One in particular is key: the role of stemmatics in OTTC. While most would recognize the value of creating a genealogical tree for the various manuscripts, in practice stemmatics has played a very minor role in OTTC for a number of reasons.
1) Very few actual manuscripts can be definitively genealogically related. There are far too many gaps in the manuscript tradition to connect all (or even many) manuscripts. This is especially true of the older witnesses.
2) When scholars have attempted to determine the genealogical relationships of ancient traditions, they have generally done so only in the most general of terms. Perhaps the SP and LXX come from an early common tradition separate from the MT? Perhaps the MT, SP, and LXX should be understood as local texts from Babylon, Palestine, and Egypt?
3) Most of the evidence from the Dead Sea region is fragmentary and difficult to use to reconstruct the textual history.
4) The variety of the ancient sources does not easily lend itself to a consistent stemmatic arrangement, but rather reflects a complex situation of mixed texts without obvious or consistent patterns.
Because of this, stemmatics have generally played very little role in the decisions of OT textual critics. Most OT textual critics approach the text from a much more eclectic perspective, picking and choosing preferred variants based on internal probabilities, rather than a reconstruction of the textual history. Whether or not this is the best solution is open for debate, but the trend does seem to be clear. In my dissertation, I will specifically be looking at the third point about the Dead Sea scrolls and what they tell us about the textual history of the OT.