Long Vedic sacrifices?

[Shrisha Rao]

Greetings.

The vArttika on the ashhTAdhyAyI of Panini, and its commentary by
Patanjali, contain a puzzling reference to certain Vedic rites that took
hundreds or thousands of years to perform:

  vArttika:  aprayukte dIrghasatravat.h  |

  bhAshhya:  yadyapi aprayuktAH avashyaM dIrghasatravallaxaNenAnuvidhaH  |
             tad.h yathA -- dIrgha satrANi varshhashatikAni
             varshhasahasrikANi cha  |  na chAdyatve kashchidapi
             Aharati  |  kevalaM R^ishhisampradAyo dharma iti kR^itvA
             yAj~nikaH shAstreNAnuvidadhate  |

Translation by Surendranath Dasgupta:

            (In the matter of the consideration of) words not in
             usage the maxim of long sacrifice applies. (To this the
             Bhasya comments) -- there are indeed words which are not
             in usage (but in this matter) the maxim of long sacrifice
             must be followed.  Thus there are indeed long sacrifices
             extending over hundred or thousand years but no one in
             these days takes to them.  The sacrificial priests give
             instructions about them only because there is merit in
             the study of the Vedas.

Source: The Mahabhasya of Patanjali: With Annotations; Ahnikas I-IV;
Surendranath Dasgupta; ed. Sibajiban Bhattacharyya; Indian Council of
Philosophical Research, New Delhi, 1991.  ISBN 81-215-0530-3, pp. 44.
(This is a late posthumous publication of a work that was left
unfinished by Dasgupta's untimely death.)

Patanjali is clearly describing a state of affairs, to wit, the
instructions by sacrificial priests of sacrifices that were impossible to
perform, which existed for all to see.  Perhaps they exist even now but
are not well known outside the community of traditional Vedic scholars.

My question therefore is: is it known exactly what sacrifices Patanjali
refers to which were (are?) covered in the teaching tradition although
never performed?  I would appreciate any references to articles or
monographs having a bearing on this issue.

Regards,

Shrisha Rao