Don't have an answer for why the recipes use terms other than the actual names of materials. The two specific ones you mention are rares, and you get them from the same harvesting nodes as the common materials. Note that there are two rares with the name oak, one is an oak root, the other is the wood rare and is called severed oak. An overview of what can be harvested where can be found here.
Ignore the "Raw" stuff .. it's just Severed Fir or Severed Oak. The "Raw" is old school stuff left over from when we had to process, treat and otherwise diddle with the crafting raws before we could actually craft the final product.
Kaisha@Permafrost wrote: We use to also get "raw" materials dropped from chests. However, the dropped materials were usually ruined items, like "broken fir banister" which could be used as a "raw fir". Dev eventually wanted to save database space and eliminated the entries for those items in the drop tables and just put the harvestable raw in its place. They also got rid of the 5 different kinds of t8 rare hides and put in "augmented hide" in its place. I remember we use to harvest Manticore, Ice Wolf, Wyvern, Dire Wolf, and...er...umm...some other hide just for tier 5 rares.
*nod* http://eq2.zam.com/wiki/A_Harvester's_Guide http://eq2.zam.com/wiki/Harvested_R...ookup_and_Guide