To put this card in context, we can look at the information pane on Fold 3. This image is from NARA microfilm publication A3355, roll 0012B, Miscellaneous Lists and Registers of German Concentration Camp Inmates, Originated or Collected by the International Tracing Service described as "Lists and Registers of German Concentration Camp Inmates, compiled 1946-1958, documenting the period 1942-1945."
These are part of a larger group of seized records, Record Group 242. A3355 consists of 189 rolls, and a roll list is available from NARA (offline). However, a roll list is available from the website of JewishGen.org, as part of Peter W. Lande's article The "Captured German Records" Collection. Be sure to read the fine print (it is a tiny font) which shows the different numbering system between NARA's copy of the microfilms versus those held at the USHMM. NARA roll 12 is part of this group of Buchenwald records:
Reels 10A-66 A3355 at NARA
This material was collected after WWII and consists of a mixture of
Buchenwald concentration records on prisoners and post-war interviews
of survivors. The entire collection is alphabetical with males listed
in USHMM Reels 29-87 (NARA 10A-62), and females USHMM Reels 88-93
The information on each prisoner/survivor varies widely, ranging from
simple basic information such as name, date of birth, category of
prisoner, and fate e.g., deceased or transferred, to detailed
information on the individual and his/her family and previous places
where that person had been held. The number of files is not known but
it clearly does not include all prisoners/survivors.
The collection is generally alphabetical though occasional files are
out of order, two reels (88 and 89) have been reversed, and Reels 66
and 67 are intermingled. All categories of prisoners are included and
these have not been separated as is true of many other collections.
Legibility is variable with the bulk of the USHMM copies in poor
shape, while the NARA copies are generally legible.
As you can see from the info pane on Fold3, Roll (12B NARA) is BLUM-BRAN.
Earlier in the article, Lande says:
There are no camp records per se for such famous concentration camps
as Auschwitz, Sachsenhausen, Stutthof (there is a separate collection
for that camp) and Neuengamme, much less the "death camps" in Eastern
Poland such as Sobibor. However, this does not mean that there is no
information on camps not directly included in the collection. This is
true since the Germans constantly transferred prisoners from camp to
camp, so that there are many lists of transfers to and from Auschwitz,
Sachsenhausen, Ravensbrück and other camps, i.e., other than the death
Unfortunately, if no records for Sachsenhausen survived, then we can't look for a corresponding arrival or departure record from there.
I was not able to find a Reference Information Paper that describes this microfilm publication on NARA's website. However, you can download RIP #(115) The Mauthausen Concentration Camp Complex: World War II and Postwar Records. Starting on printed page 328 (page 338 of the PDF), there is a list of the materials from that camp. On page 331 (page 341 of the PDF), items numbered 59 and following indicate that arrival lists and transfer lists to and from Buchenwald exist for Mauthausen. If you could locate a finding aid or discussion of the records for this camp which included a list or register from Mauthausen, and find the corresponding record for that prisoner in this collection from Fold3, that might give you enough context to interpret your cousin's record.
You could also contact NARA via the links on the page http://www.archives.gov/contact/ or email them at email@example.com.