Inherited IRA: Value of holdings on December 31st of the previous year (which is the year of death)

My siblings and I inherited a traditional IRA from our brother who passed away in March 2023.  I am an eligible designated beneficiary and so may opt to take stretch distributions over my lifetime.  If I take an RMD by 31 December of 2024, it is my understanding that the distribution will be based on the value of the holdings on 31 December, 2023 (the year of death).  

 

My brother's IRA was with 2 different firms.  The first provided us with a statement that showed the value on 31 Dec, 2023.  The second firm just provided us with statements that started on 1 January 2024, and those statements only showed an end of month balance.  (If I had the beginning balance I would know the value of the holdings on 31 Dec, 2023.)  I reached out to the second firm this morning, but didn't get a helpful reply.

 

Am I correct that I need the 31 Dec, 2023 balance to calculate my RMD?  If so, what do I  do now?