Can I still discuss real numbers with a buyer before they've signed anything?

You can, but it shifts the risk onto you in a way that's easy to avoid simply by sequencing things differently. Once specific financial numbers are shared, they can't be unshared, and if the buyer later walks away or turns out to be a competitor doing research rather than a genuine prospect, you have far less recourse without a signed agreement already in place covering what was disclosed and how it can be used.

The practical fix is sequencing, not necessarily withholding numbers forever: get a confidentiality agreement signed before, rather than after, discussing anything specific, so that if a conversation is going somewhere real, the protection is already in place the moment it matters. This doesn't need to slow things down much — a short NDA can typically be signed quickly once a buyer is genuinely engaged, and asking for it before getting into figures is a normal, expected step in a serious conversation rather than an awkward one. A Treadstone business lawyer can provide a standard agreement so you're not drafting one from scratch each time a conversation gets to this point.