The peculiar concern with the four prongs, is the inability to hold water in a tenable manner. This, we discuss in the context of four modes/means as considered by some of the śrīvaiṣṇava schools. Take for example the case of matadīpikā where the author has a two fold folder - bhaktiprapattibhyāṃ prasannaḥ sa evopāyaḥ. Insofar as the authority of it as a handbook of the school's metaphysics, its acceptance is a given.
In this as a context, one would be stretching the fabric a bit thinner than ever, to extend it out to four. Now, what the school considers as the means at times becomes befuddling.
And the onus here is in clear, on an adherent rather than the school's corpora themselves. Or, if one would allow a bit of political incorrectness, adherents who slipped a view or two.
Apropos the question of means, it is singular and not; as a good philosopher would, the tent's legs shook to hold. The school in earnest, considers īśvara as the means (differences aside on definition). Given the question of human agency and free-will, considers one of the two, to divert attention, so to speak.
Devotion (bhakti) and Surrender (prapatti) remain the two choices for the aforesaid diversion. Insofar as the definitions go and whether they are concordant is another qualm of itself. With the acceptance of the two as the modus choices, any extension is as tertiary modes. And, the painful reality here is that, a secondary modus' rejection would mean, a tertiary's too.
Extending, there is another regressus, that suffers similar fates. On the quandary of a dual positing of karma-jñāna, the school rejects it, swings different to it. Now, when the school considers the former a conduit to the latter, the four prong approach falls flat. This also does open up another can, of works or worms, on the peculiar nature of what's termed kaivalya by the school.