I sent an email to Doug Sulipa, as he had a CGC 9.2 listed and here's his response when I asked him about if the mask was loose or not and here's his response:
"Hi Greg
I imported all the Captain Britain from the UK, when they were new in 1977-1978.
I can confirm that all copies of #1 came new with the MASK Loose.
Most copies originally came with a horrible Elastic Band around the mask, some came without.
I quickly realized the Elastic Bands were damaging the comics & removed them to prevent major damage.
People who left the Elastic Band in the book saw bad indentations, stains around it, then it stuck to the paper.
If left long term, the Elastic Bands petrified, started to crumble & then became permanently embedded in the paper inside, making them Low Grade copies.
My copies all had loose Masks, with NO Elastic Bands, thus they survived in higher grades.
I have sent in about 35 Copies to CGC over the last five years & am down to my very last copies.
Thank You, Doug"
***So, it appears that CGC will just grade the books with masks loose***