As the godly know, there are few things more sublime than solid chronological work. That's what makes chapter four of Brant Pitre's Jesus and the Last Supper a thing of beauty. In this chapter Pitre addresses the ever-vexed question about the date of the last supper. He rightly notes that this question is the single most disputed chronological issue in NT studies. The issue turns upon a perceived contradiction between the accounts in the Synoptic Gospels, which indicate that the Last Supper took place on 15 Nisan, and the account in John's, which is typically thought to indicate that it took place a day earlier, on 14 Nisan. This perceived contradiction has become a significant point of contention in New Testament scholarship, as 15 Nisan is typically identified as being self-identical with Passover. The questions of whether the Last Supper was a Passover meal and whether Jesus was understood as a Passover sacrifice are both related integrally to this matter. Pitre's contribution is to show that the historical problem is based wholly upon questionable exegesis.
Pitre argues that scholarship has made the error of supposing that in all cases, when the gospels refer to Passover, they are referring to 15 Nisan. Against this, he argues that in late Second Temple Judaism, "Passover" could refer to at least four different things: the Passover lamb, sacrificed on 14 Nisan; the Passover meal on 15 Nisan, at which the lamb was consumed; the Passover peace offering, consumed over the period from 15-21 Nisan; or Passover week, also from 15-21 Nisan. Without getting into the complicated details, which span more than forty pages in Pitre's work, suffice it to say that he demonstrates quite persuasively that when the differing uses of the term are kept in mind, the appearance of contradictory claims between the Synoptics and John evaporates.
In Lonergan terms, what Pitre has done is recognize that interpretation must precede history. Before one can on the basis of ancient texts infer what happened in the past, one must first establish what said texts actually say on the relevant matter. The question "On the date of the Last Supper, is John correct or are the Synoptics?" is meaningful only if John and the Synoptics diverge on the dates that they report for the event. If they converge then certainly one can still ask whether or not Jesus ate his Last Supper on the date mutually indicated (Pitre argues that this date is 15 Nisan), but the question of whether to prefer John or the Synoptics becomes meaningless as there is no substantive difference. The historical problem--whether real or chimerical--is entirely the fruit of exegesis.
Incidentally, the potential objection that Pitre is "conflating" texts holds no water, as it supposes what remains to be proven, namely that the texts present divergent data on the matter of the Last Supper's date. If exegesis demonstrates that they do not, then no conflation is possible because there is nothing to conflate. If exegesis demonstrates that they do, then no conflation has occurred because one recognizes that they diverge. Also incidentally, of course our understanding about the possible meanings of the term "Passover" is itself the fruit of previous work. That literally goes without saying, and entails nothing more than the paired and really quite banal insights that one never comes to any question with an empty head and that what fills one's head is the fruit of previous discoveries.