First you said that the GIA listed the table as 67%, and then you said 61.6%?
Regardless, either of these measurements is a BIG difference between what the cert states and what the independents are telling you. The difference between 61.6% and 72% is HUGE.
Yes, I would be concerned. GIA makes mistakes, but this one would be quite unusual.
A GIA certed stone always brings a premium because it has a cert. If that cert is not proper, or not the right cert, the stone should be cheaper or the mistake should be corrected.
I would call GIA (or have your jeweler call them), and ask them what's up. See if they have a clue, or if they'll re-check the stone for you at no charge.
Now, an additional problem. If the stone is a 61.6% table, great. If it's a 67% table.....well okay...maybe. If it's a 72% table, that's considered a "spread" crown. Not considered a desirable characteristic. A 72% table is usually accompanied by a lack of "fire" (dispersive colored light return). Often there will be a very thin to extremely thin girdle as well, which makes it susceptible to nicking and chipping over the years.
Post all the characteristics so we can muse on it for a while...
Rich, GG
Sarasota Gemological Laboratory