Hi Howard,
I think you are referring to page 20 of the introduction. (see the following excerpt below).  There are 27 references to aucitya in the critical edition of Ingalls et al.  I've attached a text version from archive.org  which you can search for "aucitya". Its a bit garbled since its from an OCR but you can use it to locate the term and then look at the print version.
Harry Spier
20 Introduction 

. . .

The literary piece must exhibit appropriateness (aucitya). To begin 
with, the plot must be appropriate to the emotions, the determinants, 
and the consequents which are to produce the intended rasa. In ex- 
hibiting the heroism of a human king, for example, one should not 
engage him in adventures that could be accomplished only by a god 
(3.10-14 A). If a plot as given in the epics and Puranas contains a trait 
that is inappropriate to the character of the hero or to the intended 
rasa, one must either omit it or add some element to the plot to achieve 
the needed appropriateness (3.10-14e A). In this regard Ananda cites 
Kalidasa as an example to be followed. His reference is in general terms 
only, but we might supply such a specific instance as the Sakuntala, 
where in the epic prototype the king abandons with needless cruelty the 
heroine whom he has seduced.’ Such action would be inappropriate to . . .
Harry Spier


On Sun, Mar 31, 2024 at 9:53 PM Howard Resnick via INDOLOGY <indology@list.indology.info> wrote:
Dear Scholars,

In the Harvard Press edition of Ānandavardhana’s Dhvanyāloka, I recall reading a passage stating, basically, that in the presentation of Mahābhārata stories, one can employ the principle of aucitya (MW: fitness, suitableness, decorum) to bring about a suitable rasa that the audience will understand and feel. Further, one may adjust or alter certain details in the MBh in order to bring this about this effect.

Presumably a famous example of this would be the various presentations of the Śakuntalā story.

I have been unable to find the passage that, I believe, states this principle of aucitya. I would be grateful for any help in tracking this down.

With best wishes,
Howard

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