The 2nd-round errata added a new feature for Alchemists, to make up for their low number of infused reagents at low level.
Your research field adds a number of formulas to your formula book; these are your signature items. When using a batch of infused reagents to create your signature items using advanced alchemy, you create three items instead of two. Each time you gain a level, you can swap one of your signature items with another formula in your formula book. This new signature item must be on your research field’s list of possible signature items.
The last sentence comes across just fine for all the research fields... except the Chirurgeon. Let's compare.
- Bomber: Begin with two 1st-level bomb formulas.
- Chirurgeon: Begin with two formulas out of a list of three.
- Mutagenist: Begin with two 1st-level mutagens.
- Toxicologist: Begin with two 1st-level alchemical poisons.
Now, the problem here is that the "list of possible signature items" isn't clearly defined. By RAW, it is only the 1st-level alchemical items of each field's specialty. Except for the much-maligned Chirurgeon, who only has three to pick from. And their Field Discovery at level 5 makes it so that one of those is permanently gaining the same benefit.
So what's missing? Clarification.
Does an Alchemist's list of potential signature formulas include all formulas of the class that matches their research field? In other words, can a Bomber pick any alchemical bombs as he advances, or is he limited to only the 1st-level list? Was a Chirurgeon supposed to be able to make any elixirs signature formulas, or is he limited to only the three he can pick from?
On that subject, why isn't the Chirurgeon able to pick any other elixirs to start? Why don't they get a list to pick from for their Perpetual Infusion ability? Everyone else does, but they only get two.