There are a couple sides to this. No company should or will tell every financial detail to every candidate. On the other hand, if a company has given you an offer and really wants to hire you, yet is very evasive about all the info you need to evaluate your offer, it can be a warning sign; it's likely indicative of the level of transparency you'll get as an employee, too. The 409A is material to understand your stock options, so very fair to ask about before signing.

Also—we'd love more questions like this in the marginal notes in the Guide, so it improves iteratively! If you (or anyone else) wants early access to that feature shoot an e-mail to josh@holloway.com