परोक्षे लिट्

The affix लिट् (Perfect Tense) comes after the verb in the sense of the past before the commencement of the current day and unperceived by the narrator.
The word परोक्ष 'unperceived' qualifies the words भूत 'past' and अनद्यतन 'non-current day' understood in this aphorism.

Well, are not the senses of verbs all unperceived, since they are mere words, and words cannot be perceived ? Exactly so; but in popular phraseology, the perception is imagined to attach to the agent with regard to certain verbs; this rule relates to cases where such perception does not take place. As, चकार 'he did'; जहार 'he took'.

It is evident that the लिट् (perfect) should not be used in the first person, i. e. when the agent of the action is the speaker or writer himself; for it is impossible that the action should not have been witnessed by him. But if by reason of some distracted, unconscious or absent state of mind, it is possible for the agent to speak of the action as one, of which he was not a conscious witness, the perfect may be used even in the first person. As सुप्तोऽहं किल विललाप 'indeed I prated while asleep'.

Vart:- The perfect should be employed (in denoting past time simply, whether of the current day or otherwise, and whether the action has been witnessed personally or not) if the sense is total denial of the action. As कलिङ्गेषु स्थितोऽसि ? नाहं कलिङ्गम् जगाम 'did you live in the Kalinga country ? I did not even go to the Kalinga country'; दक्षिणापथं प्रविष्टोऽसि ? नाहं दक्षिणापथं प्रविवेश.