For smelting iron, you need a fuel that's nearly pure carbon, which has typically been either charcoal or coal. The former is the more easily obtained; when the forests were too depleted to provide adequate supplies of charcoal, people started mining coal on a large scale.
Is it actually the case that charcoal is as good as the best coal, so that in a setting where adequate supplies of the former still exist, there would be no reason to start mining the latter, and a setting that was deficient in coal, would only be a hindrance when the forests started running out?
In particular, I noticed in an answer to How far could civilisation develop within one lifetime - starting from nothing?
anthracite coal. This allows you to fire kilns to a sufficiently high temperature to make steel.
I would be surprised if that implied anthracite is better than charcoal, which is as I understand it also pretty much pure carbon. But perhaps it just implies 'given that the forests are depleted and you have to switch to coal, you are much better off with anthracite, which is pure enough to fully substitute for charcoal, instead of having to burn something lower grade like lignite'?