^Yes, but my thinking is that such a procedure might not have been total, and that the kinds of digital technology we have today might be able to extract information that would've seemed to be completely erased by the standards of 1970s/80s analog technology.
After all, the Reconstruction Team was able to extract that color information from black-and-white copies
of the originals. The copying equipment wasn't designed or set up to transfer any color information to the copies at all, yet somehow a trace of such information was transferred over anyway, which is amazing to me. And people working with modern computers were able to extract those fragments of information, interpolate what was missing, and combine it with the existing monochrome information and photo reference to reconstruct what had been lost. So if such hidden information could be found in a copy
that wasn't supposed to contain any of it at all, then who knows what leftover bits might linger on the originals, despite the best efforts of '70s technology to eradicate them? It might just seem to be random specks of noise, but a powerful enough computer might be able to divine a residual pattern. And maybe at least a partial reconstruction could be achieved by using the existing stills and clips as reference to help interpolate the missing image information. (For instance, if you know that the pattern of magnetic traces on frame X corresponds to such-and-such a frame capture of the Doctor in a particular pose, then understanding the pattern beneath those traces could let you deduce that the traces in a subsequent frame correspond to the Doctor having moved a foot to the left. And so on.)
So no, it's not a sure thing -- in fact, it's a heck of a reach. But most anyone would've thought it was impossible to reconstruct the color information from those Third Doctor episodes, yet it was done. So at least it would be worth looking into this, trying to track down the original tapes and seeing if
there was a way to extract useful information from them. No harm in trying, right?