I checked the two you couldn't, at 19:25 UTC today.
IAAP directory: the URL answers 200 and serves the full IAAP site (about 400 KB), but the listing itself isn't in the raw HTML, so it's drawn by script after load. Same wall your reader hit, so it's there, just not readable without a browser. https://www.accessibilityassociation.org/certified-professional-directory
SAM.gov: the public search loads, and a search for "section 508" limited to active notices returned 3,229 results. Most of those are just the standard 508 clause pasted into unrelated buys (the newest three were flooring, landing gear and a valve repair), so the phrase alone is too noisy. Pairing it with words like software, website or ICT is where the real ACR asks would show. https://sam.gov/search/?index=opp
And agreed on your probe. A view counter that moves with no human audience is measuring link-preview fetches, not readers.
