Query: is The New Liturgical Movement doing a series, or is it not, which will come to a conclusion, on whether the Roman Rite originally had three readings (including the OT) at most Masses? I'm a trifle puzzled.
In Liturgy there often tend to be lots of funny little clues which point to elements which have got lost. I do not know of any such tasty little clues to support the hypothesis of the Lost OT Reading*. I suspect that, quite simply, at some early point somebody/bodies in Rome decided that it would be NT nearly always on Sundays/festivals, with OT on fasting ferias/vigils etc., and in the Divine Office. (Such a system, of course, would be expected to become gradually eroded and 'exceptions' would enter the rite; Masses of our Lady spring to mind.) Substantially, this is very much what we still have now, and very neat it is. And it supplies a very Rich Table of OT Scripture.
I think the way forward might be the re-examination of Patristic remarks about Scripture to see whether there is any evidence of a rationale being offered for such a practice. The reason why this has never been done is that nearly everybody has blindly accepted the unevidenced theory of the Missing OT Reading at Rome.
I would be interested if my erudite readership had any ideas.
*Except, just possibly, the presence of two psalms after the Epistle. But this would point to the 'missing' reading having come between the Epistle and the Gospel.