Criteria for denoting unknown data in cosmic db

Question

[Peavil]

I am wondering the criteria for denoting unknown data in cosmic db.

for example PIK3CA gene,

Accession Number    Gene CDS length HGNC ID Sample name ID_sample   ID_tumour   Primary site    Site subtype 1  Site subtype 2  Site subtype 3  Primary histology   Histology subtype 1 Histology subtype 2 Histology subtype 3 Genome-wide screen  Mutation ID Mutation CDS    Mutation AA Mutation Description

NM_006218.1 3207    8975    2493513 2493513 2356117 breast  NS  NS  NS  carcinoma   NS  NS  NS  n   COSM29325   c.? p.H1047R

NM_006218.1 3207    8975    1670204 1670204 1583490 breast  NS  NS  NS  carcinoma   NS  NS  NS  n   COSM775 c.3140A>G   p.H1047R    Substitution - Missense

These two data seem to be similar. Even Mutation AA (Amino acid) has the same value(p.H1047R), the below data has the cds number(c.3140A>G), and the above data shows that the cds number is unknown(c.?).

I wonder why I know the "mutation AA information" but the cds information is unknown.