Get OpenFl version for html build

Is there a way to tell which version of OpenFl was used in a html5 build from the files generated by the build?

Sure! You can haxe.macro.Compiler.getDefine to cook any defined Haxe value into the compiled output:

import haxe.macro.Compiler;

...

var openflVersion = Compiler.getDefine("openfl");

I was asking for builds that have already been made. And I was able to find it. The debug.hxml file in the html5/haxe folder contains these lines:

-D openfl=8.8.0
-D lime=7.2.1

I was looking only in the files in the bin folder which is the actual html5 folder created by a build.