I had an earlier post on Tracking Down Similarities Between the NT and the Apostolic Fathers. I suppose this is a continuation of that post.

This is from the Edito Critica Maior edition of James (Volume IV, Installment I, Part 1). Note that the ECM's interest is in Patristic citations of the NT and they are not specifically focused on the writings of the Apostolic Fathers, as I am. So their pool is wider and deeper. But still, here is their definition:

The difficulty of distinguishing true quotations from allusions or paraphrases is well known. Considering the great mass of the variant readings found in the manuscript tradition of the first millennium and recorded in the present edition, the following rule of thumb is observed: a true quotation is one where the wording of the Father's text is identical with a reading found in the manuscript tradition. Readings attested exclusively by a Father are only rarely recorded. Allusions are considered only if they clearly reflect a known reading. Variants are excluded from the apparatus if they may be ascribed to a Father's stylistic tendencies and are unlikely to have been in his manuscript source. In essence, the criteria for patristic quotations are restrictive in order to ensure their reliability. (ECM IV.I.1, p. 12*-13*)

So, in essence, the rule is restrictive. Data from the Fathers can only be used as support for existing readings, not as datapoints of new and heretofore-unknown readings. You have to draw the line somewhere, and I can see why it was drawn there.

Of course, with that rule, there will be very little if anything from the Apostolic Fathers that plays a part in the apparatus of the ECM (and, thus, NA28). Some, yes. But not a lot.

But, on the flip side, if you're looking for patristic citations in general, then you need to add examining the ECM to your list. Oh, and since my last post I've been able to consult some volumes of Biblia Patristica, and you need to add those to your list too.