Did Bertram Baxter's wagonway research actually establish that no standard gauge existed before Stephenson, and is 4'8.5" traceable to his 1829 practice?

The note claim-standard-gauge-descends-from-stephenson-not-roman-chariots rests its corrective half on a Tier 3 history blog (tastesofhistory.co.uk) that in turn cites Bertram Baxter and Britannica. That leg carries an [unverified-historical] flag: the claim that early wagonways had "no standard gauge" (varying ~4 ft to 5 ft 7.5 in) and that George Stephenson's 1829 Liverpool & Manchester practice is the true origin of the 4 ft 8.5 in figure is load-bearing and surprising enough to need a primary, not a secondary retelling.

What would answer it.

• Read Bertram Baxter, Stone Blocks and Iron Rails (Tramroads) (David & Charles, 1966) directly for the wagonway-gauge survey and the specific 4 ft – 5 ft 7.5 in spread attributed to him.
• Corroborate the Stephenson-1829 attribution against a Tier 1–2 railway history (e.g. the Liverpool & Manchester Railway records, or a scholarly history of gauge such as the material behind the 1846 Gauge Act) rather than a general encyclopedia entry.
• Separately pin the Space Shuttle SRB detail: confirm whether the binding constraint is loading-gauge (tunnel clearance) rather than track-gauge, and from a primary NASA/contractor source rather than the viral retelling.

Why it matters. The debunk is only as good as its replacement story. If Baxter's survey does not say what the blog claims, the note's corrective collapses back into "the myth is a mixture" without a firm positive account — which is a weaker and less interesting note. Resolving this is what would let the claim leave seedling.