Again from the Dec.8 news release:

"In light of the preliminary results which strongly suggest the presence of additional platinum group elements, specifically, rhodium, iridium, osmium, ruthenium and rhenium;"

When they say 'Group' they mean that these metals are related chemicly (i.e. they have very similar structure and therefore chemistry ). If one is found then there are very good odds that some of the others will also be found.

They were not checked for before because they were not expected ( similar to hole 49) but having found rhodium, they are assaying for the others also.