As per conversation with Chris, the obsolete Iron compound should be the first one (cpd00021) because it's not used in the templates whilst the second (cpd10515) is.
It raises an important question about how template development should occur independently of biochemistry curation for the time being.
I'm closing this one because by double-checking aliases and structures, I've found that the two compounds in question are in fact not the same (and thus not obsolete).
As per conversation with Chris, the obsolete Iron compound should be the first one (cpd00021) because it's not used in the templates whilst the second (cpd10515) is.
It raises an important question about how template development should occur independently of biochemistry curation for the time being.