From the picture on your link the test certificate says only 200 bar working pressure.....
Isn't that a bit low?????
Only tanks I've ever seen used in the paintball circle are 232 and 300 bar versions.
It does look pretty good condition from the picture... but....... IMO, I'd have left this alone. I mean, last test was 99 which, at very best, would mean that it was made in '96, which makes it 8 years old with not a scratch on it .........
Looks like a new paint job to me. Especially and you say you can hardly see the markings.
But then I'm not an expert.