At the beginning of his Seśvaramīmāṃsā, Veṅkaṭanātha tries to synthetise what he (and Rāmānuja) calls Pūrva and Uttara Mīmāṃsā, with the further addition of the Devatā Mīmāṃsā.
In this connection he needs to address an apparent divergence, namely that between the siddha and sādhya interpretation of the Veda. In other words: Does the Veda always convey something to be done? Or does it always convey something established? The unity of the three Mīmāṃsās and of the Veda as their basis does not allow for a different interpretation of the statements in the Upaniṣads and in the Brāhmaṇas.

Veṅkaṭanātha cites Rāmānuja in order to show that there is no real opposition and that the sādhya-aspect is parasitical upon a siddha one. The example he reuses from Rāmānuja is that of taking action in regard to a hidden treasure: One starts acting only after having known that the treasure is really there. Thus, the sādhya element (taking action) depends on the siddha one (the acquired cognition of something existing).

At this point he also quotes from anoter Vaiṣṇava author, namely Parāśara Bhaṭṭa. His Bhagavadguṇadarpaṇa is a commmentary on the Viṣṇusahasranāma and here comes the quote:

bhagavadguṇadarpaṇe hi phalopāyaṃ prastutyoktam “sa ca siddhaḥ sādhyaḥ sālambanarūpaś ca. siddhas tv ārādhyamānatayā phalapradā devatā” ityādi.

For, in the Bhagavadguṇadarpaṇa (by Parāśara Bhaṭṭa) after having raised the topic of the instrument to the result it is said: “And this (tool to the result) is established (i.e., it is the deity), it is to be established (i.e., it is the karman) and it has the form of being with a support (ālambana).”

What is the sālambanarūpa ‘having the form of being with a support’? This last specification seems to refer to the brahman, since it is the missing part, perhaps in the sense that the brahman is the support (i.e., the culmination) of everything else. In this way, Veṅkaṭanātha would also interpret Parāśara Bhaṭṭa as supporting the idea of the threefold Mīmāṃsāśāstra.

However, a further enigma regards the reading of the text itself. All manuscripts read sa ca siddhaḥ sādhyālambanarūpaś ca. Does it mean that there was only a bipartition and not a tripartition, i.e., the tool for the result could be siddha or have a sādhya support? This seems like a plausible reading, but why would have then the editor of the 1971 edition emended the text as reproduced above? Did he do it according to the published text of the Bhagavadguṇadarpaṇa?

Do readers know the relevant passage of the Bhagavadguṇadarpaṇa? (I failed to locate it).