2nd Sunday of Advent / Feast of the Immaculate Conception at TLM?

Hello Reverend Father(s), hope you are having a great day!

Since, during Advent and Lent, Sundays “outrank” Solemnities, the Feast of the Immaculate Conception is transferred to Monday, December 9th. As such, in the Novus Ordo, both Sunday and Monday are Holy Days of Obligation.

However, I was planning on attending this Sunday’s Mass at an ICKSP Parish (Traditional Latin Mass). In the bulletin, it says that their 10:00 AM High Mass (as well as all other Masses on that day) is the “Immaculate Conception of Mary, Commemoration of the Second Sunday of Advent”.

I was wondering if this means that the Mass is valid for both the Second Sunday, and the Immaculate Conception, or if I have to attend a different Mass on Monday to fulfill my obligation (the TLM has no Monday Mass for the Immaculate Conception, so I assume the former is true).

Thank you for your time,

Pax Vobiscum.