Was the episode of an attempt to dis-robe Draupadi an interpolated story?

I doubt it.

If we study subsequent Parvas/chapters in Mahabharata, there was a mention of dragging of Draupadi in the Royal Assembly when she was in her periods. However, there was no mention of dis-robing of Draupadi.

Consider the following 2 incidents:

1) Immediately after Pandavas going to the Forest, for completion of 12 years of exile period and 1 year to be lived incognito, Sanjaya admonishes the King Dhritarashtra for his folly in not stopping his foolish son Duryodhana.

Hence, Sanjaya did not mention about an attempt to dis-robe Draupadi.

āsāditam idaṃ ghoraṃ tumulaṃ lomaharṣaṇam

pāñcālīm apakarṣadbhiḥ sabhāmadhye tapasvinīm

ayonijāṃ rūpavatīṃ kule jātāṃ vibhāvarīm

ko nu tāṃ sarvadharmajñāṃ paribhūya yaśasvinīm

paryānayet sabhāmadhyam ṛte durdyūta devinam

strī dharmiṇīṃ varārohāṃ śonitena samukṣitā

ekavastrāṃ ca pāñcālīṃ pāṇḍavān abhyavekṣatīm

hṛtasvān bhraṣṭacittāṃs tān hṛtadārān hṛtaśriyaḥ

vihīnān sarvakāmebhyo dāsabhāvavaśaṃ gatān

dharmapāśaparikṣiptān aśaktān iva vikrame

kruddhām amarṣitāṃ kṛṣṇāṃ duḥkhitāṃ kurusaṃsadi

duryodhanaś ca karṇaś ca kaṭukāny abhyabhāṣatām

The wretches have brought on themselves this terrible, wholesale, and horrible destruction by dragging the helpless princess of Panchala into the court.

Who else than Duryodhana--that false player of dice could bring into the assembly, with insults, the daughter of Drupada, endued with beauty and intelligence, and conversant with every rule of morality and duty, and sprung not from any woman's womb but from the sacred fire?

The handsome Krishna, then in her season, attired in one piece of stained cloth when brought into the court cast her eyes upon the Pandavas. She beheld them, however, robbed of their wealth, of their kingdom, of even their attire, of their beauty, of every enjoyment, and plunged into a state of bondage.

Bound by the tie of virtue, they were then unable to exert their prowess. And before all the assembled kings Duryodhana and Karna spake cruel and harsh words unto the distressed and enraged Krishna undeserving of such treatment.

2) In Virata Parva, after getting humiliated by Kichaka in the Royal assembly of Virata, Draupadi reaches Bhima’s place in the night and narrates her predicaments.

Then she recollects what happened in Hastinapura, after Yudhisthira got lost in the game of dice. She said that she was dragged to Assembly by Pratikami, but not Dushasana.

She even mentions about the second insult due to Saindhava/Jayadratha, but not about dis-robing incident.

yan māṃ dāsī pravādena prātikāmī tadānayat
sabhāyāṃ pārṣado madhye tan māṃ dahati bhārata

vanavāsa gatāyāś ca saindhavena durātmanā
parāmarśaṃ dvitīyaṃ ca soḍhum utsahate nu kā

The Pratikamin dragged me to the court in the midst of an assembly of courtiers, calling me a slave. That grief, O Bharata, consumeth me. What other princess, save Draupadi, would live having suffered such intense misery? Who else, save myself, could bear such second insult as the wicked Saindhava offered me while residing in the forest?

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Hence, the inference would be that the episode of an attempt to dis-robe Draupadi was an interpolated story.

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Here, a question may arise as to why the interpolated story of an attempt to dis-robe Draupadi was included?

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If we carefully study the episode of an attempt to dis-robe Draupadi, we can find that it was included to elevate Shri Krishna, who was described by Sage Vyasa as a great warrior and schemer, as an incarnation of Vishnu.

In the interpolated story, when Dushasana tried to dis-robe Draupadi, she prays to Shri Krishna as Sri Hari (Vishnu).

Then Dussasana, O king, forcibly seizing Draupadi's attire before the eyes of all, began to drag it off her person."

Vaisampayana continued,--

"When the attire of Draupadi was being thus dragged, the thought of Hari, (And she herself cried aloud, saying), 'O Govinda, O thou who dwellest in Dwaraka, O Krishna, O thou who art fond of cow-herdesses (of Vrindavana). O Kesava, seest thou not that the Kauravas are humiliating me. O Lord, O husband of Lakshmi, O Lord of Vraja (Vrindavana), O destroyer of all afflictions, O Janarddana, rescue me who am sinking in the Kaurava Ocean. O Krishna, O Krishna, O thou great yogin, thou soul of the universe, Thou creator of all things, O Govinda, save me who am distressed,--who am losing my senses in the midst of the Kurus.'