Answer

In the Jain calendar, some tithis can be skipped (kṣaya tithi) and some can repeat as double tithi (vṛddhi tithi) because tithi is based on the movement of the Moon and Sun.

However, traditionally in Jain practice, the most important rule is:

• Pakkhi / Pakṣik Pratikraman is done on Chaudas or Poonam / Amas depending on tradition and calendar adjustment.
• Samvatsari Pratikraman is never simply omitted; if there is a tithi complication, Jain calendar rules decide the proper observance day.
• Paryushan / Das Lakshan observances are adjusted by the Jain pañchāng according to accepted rules.

Explanation

A lunar tithi is not exactly equal to a civil sunrise-to-sunrise day. Because of this:

• Skipped tithi / Kṣaya tithi: A tithi begins and ends between two sunrises, so it does not appear at sunrise on any civil day.
• Double tithi / Vṛddhi tithi: The same tithi is present at sunrise on two consecutive days, so it appears twice.

So technically, many tithis can become skipped or repeated depending on astronomical calculation.

Important Jain Understanding

In Jain Dharma, religious observances are not decided casually. They are followed according to the Jain pañchāng and the guidance of the proper Jain tradition.

For example:

• If a tithi is skipped, the observance may be shifted according to established rules.
• If a tithi is doubled, rules decide whether the first or second occurrence is used.
• Different Jain traditions may follow slightly different calendar rules.

Takeaway

There is no simple universal list that says “these tithis are never skipped” in ordinary calendar astronomy. Tithis can be skipped or repeated due to lunar motion, but Jain religious observances are protected by traditional pañchāng rules so that important duties like Pratikraman and festival observances are properly maintained.