Thanks everyone for the replies.
So, for the problematic files, I need to convert them to flacs using an external program and then bring them to picard to tag.
Before, I do this, are there any other programs which do this magic with wave files ?
I am slightly older gen audiophile who used to play cds off a Transport > Dac. So, all this is new to me.
Also, when picard write the tag info to the flac files, does it modify the flac file in any way ?