by reading PRJ / similar files associated with ECW, if they exist, and using their info to override the coordinate system stored in ECW.
The fundamental problem, it seems, is an ECW that specifies a slightly inaccurate coordinate system.
I'm not 100% convinced that is what is going on in this particular instance (I've uploaded the ECW with a detailed report to tech support, so they can see if Manifold is failing to import some coordinate system details from the ECW that it should). But based on the extensive detail in the coordinate system (drill into the base, etc., etc., to see) you get with the import it seems that Manifold is correctly harvesting all coordinate system info the ECW says. So let's go with that as a working hypothesis.
As I mentioned in my other post, in the past there have been instances of ESRI people using PRJ files to get around ESRI inability to read coordinate systems specified by the ECW. Some of that may have been because ECWs have a limited ability to specify coordinate systems.
An ECW does not have the internal ability to specify all projections that can be handled either by ESRI or by Manifold. I suspect the ESRI community's use of PRJ files as a non-standard sidecar file to override whatever is in the ECW evolved as a way to specify projections used that the ECW standard itself could not handle. That is just a guess. [From a purely anthropological perspective it's a plausible guess, since ESRI people evolved PRJ files to get around the inability of shapefiles to specify projections... so why not apply the same kludge to other formats?]
If that guess is true, using a PRJ file to override what is in the ECW is a wretched kludge, a truly irresponsible way of using ECW, because it means you are willing to write an ECW that contains fake projection data, that tells a lie. Sooner or later that fake info in the ECW is going to cascade into yet more inaccurate work products created from that wrong ECW file. The right way to use ECW is to re-project your image into whatever projection an ECW can handle, and not to use a PRJ file to override wrong info deliberately placed into the ECW.
I strongly disagree that Manifold should say "we support ECW format" and then ignore what the format says. I understand the argument that if somebody did not want a PRJ to override what the ECW says, they wouldn't put a PRJ in the same folder as the ECW. But that assumes people understand that ECW doesn't use PRJ so having a PRJ is an override. What if in the same folder they had a different image format that does use a PRJ with the same stem, prior to re-projecting into a projection that ECW could handle?
In that case, by assuming the user does not want to respect the ECW standard, automatic use of PRJ to override would get it wrong. Such second guessing of users that when they explicitly say to use a standard, like ECW, they should not be trusted, well, such disrespect for what users say they want to do is a formula for chaos.
Look, if the problem is that an ECW has an error in it, specifying the wrong coordinate system, the solution is to make it easier to fix that error. There are three ways to do that:
a. The existing way: If you think the ECW you have needs a repair to the coordinate system because the wrong one was specified in the ECW file, you choose Repair Coordinate system, drill down to the Coordinate System dialog, and in one click choose the right system. This isn't rocket science.
b. If you want to consume a PRJ file, OK. Add that as another tab to the Coordinate System dialog, so in addition to Standard, EPSG, and Custom, you also have an Import tab. If you want to repair a wrong coordinate system specified by the ECW, you now have a fourth choice, of harvesting a coordinate system from a PRJ file, or from other sources. You could click the Import tab and get a dialog for importing the coordinate system from various different sources: pick some other component in your project, or choose a TFW file, or paste a JSON specification, or... (drumroll...) pick a PRJ file.
c. Less pretty, because it wrecks the simplicity and ease of use of automatic imports using file extensions, is to have a separate ECW import dialog that provides a checkbox captioned: "Override ECW coordinate system with PRJ file."
Personally, I don't like c. because I think it's a mess to wreck a clean, easy to use dialog with a special case control that works only when the format contains fake data. Deliberate misuse of a format is a fairly rare thing, so it seems that b. above would be the better way. Why punish everybody with a complication because a very tiny minority of users deliberately wreck a perfectly good format?