We can't-- at least not dependably.  Download a batch of wav files for your project.  How many of them work?  How many won't work?  There's no way to know without attempting to load and manually test each one, and who wants to do that??

A Bastardized Standard
The WAVE format is sort of a bastardized standard that was concocted by too many "cooks" who didn't properly coordinate the addition of "ingredients" to the "soup". Unlike with the AIFF standard which was mostly designed by a small, coordinated group, the WAVE format has had all manner of much-too-independent, uncoordinated aberrations inflicted upon it. The net result is that there are far too many chunks that may be found in a WAVE file -- many of them duplicating the same information found in other chunks (but in an unnecessarily different way) simply because there have been too many programmers who took too many liberties with unilaterally adding their own additions to the WAVE format without properly coming to a concensus of what everyone else needed (and therefore it encouraged an "every man for himself" attitude toward adding things to this "standard"). One example is the Instrument chunk versus the Sampler chunk. Another example is the Note versus Label chunks in an Associated Data List. I don't even want to get into the totally irresponsible proliferation of compressed formats. (ie, It seems like everyone and his pet Dachshound has come up with some compressed version of storing wave data -- like we need 100 different ways to do that). Furthermore, there are lots of inconsistencies, for example how 8-bit data is unsigned, but 16-bit data is signed.

I've attempted to document only those aspects that you're very likely to encounter in a WAVE file. I suggest that you concentrate upon these and refuse to support the work of programmers who feel the need to deviate from a standard with inconsistent, proprietary, self-serving, unnecessary extensions. Please do your part to rein in half-assed programming.

but with QB64 -- and that's with the fact that these are WAV files which we *should* be able to work with, but we can't. 

I think it's the same between two + and/or - operators, left to right = right to left.

eg /2 is same as *.5

Well! In this case I was not asking for a solution, I was pointing out a fact.
And "stupidly" I thought it could be useful to someone.

About the solution was intuitive. Yes, but only after understanding that "+" disturbs the interpreter. Normally why should I worry about the folder name affecting the result of the routine?

Anyway thanks for your attention.