Should I worry about a buyer forwarding my information to their own investors?

It's a reasonable thing to think about in advance rather than discover after the fact, particularly if the buyer is backed by outside financing or a group of investors rather than buying with their own funds alone. A confidentiality agreement that only names the buyer personally may not clearly cover investors the buyer brings in to help fund or evaluate the deal, leaving a gap in exactly the situation you're worried about.

The fix is straightforward: make sure your NDA's definition of who's bound extends to the buyer's financing sources and investors, either by including them within a broadly defined "representatives" clause with the buyer remaining responsible for their compliance, or by requiring specific investors to sign their own acknowledgment before receiving anything sensitive. Ask the buyer directly, early on, whether investors or a financing partner will need to see your information, so you can address it in the agreement rather than learning about it after documents have already gone out. A Treadstone business lawyer can build this into the NDA before you're deep into sharing sensitive material.