Nearly all clarity enhanced diamonds which are glass in-filled begin life as Imperfect clarity diamonds. The sellers tend to grade their clarity as they appear after the glass filling without taking into account the structural integrity, or lack of structural integrity of the enhanced diamond. They are putting the very best picture forward and no one seems willing to make an issue of it. Some glass in-filled diamonds do begin as SI or a rare one might get as far as VS diamond, but I doubt anyone has ever begun with a VVS diamond because there would never be a reason to "improve" such a high clarity stone.
Most of the selling of these diamonds is smoke and mirrors and much of the sales pitches are outright fraud. The informed who buy such diamonds are getting a pretty thing but they are aware of what they are buying. Far more unaware people buy them and do not understand the nature of their purchase. So long as they are happy I suppose there is no problem.
If a diamond which is glass in-filled looks like a VVS clarity after filling it would be a very rare one, but I suppose an unusual situation is possible although highly unlikely. I''d suggest such a statement is more likely a sales pitch and to be doubted until proven correct by independent examination. When you buy enhanced diamonds with glass in them, one must accept a high degree of imperfection exists in the stone which is simply less visible. It doesn''t change anything material, but it may be just what someone wants to fit their budget and desires.