"Prolog" is like Lisp, a wide array of superficially similar languages that actually are quite diverse.
Mind you, in that sense, Java and C# are more or less the same language, which has Prolog programmers nodding their heads and Java and C# developers screaming.
Nope. Prolog is an ISO-standardized language since 1995 and the spec was updated in 2012. Where older "legacy" Prolog implementations such as SWI, YAP, and SICStus are deviating from the standard is generally pretty well-known to Prolog practitioners, and the convener of ISO 13211 actually can verify claims of ISO conformance; for example, [1] is a link to the ISO certification of Quantum Prolog (the web app at [2]).
It's true however that people are quick to conflate Prolog with constraint-logic programming libs, "expert systems" (RETE-style forward-chainging systems and other "rule engines"), or random "functional-logic" programming languages. The misunderstanding of PROLOG and logic by Lisp programmers has been ongoing since the 1980s, probably because at one point Prolog and Lisp were seen as competing "languages for AI" for some reason even though they have very little in common.
[1]: http://www.complang.tuwien.ac.at/ulrich/quantum-prolog/
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