Build it bottom-up from a counted account universe that matches your ICP definition, priced at your actual realised ACV by segment — not top-down from an analyst market figure. A TAM you can enumerate is a target list; a TAM you can only cite is a slide.
The bottom-up version has a second payoff: the same scored universe becomes the territory input and the outbound target list, so the work is reused rather than done once for a fundraise. State the counting method and the ACV basis alongside the number.
Every claim above comes from work LeanScale published. These are the sources.