Clayton,
You are correct in your assumption. As a CWI, you can witness a welded coupon, and witness and perform the bend test specimens per D1.1. In fact, some CWI's do this as a business along with consulting, writing weld procedure specifications, etc. Al made a good point about the WPS, and, usually, should a certified welder's employment cease with a particular company, for whatever reason, it is my experience that most companies don't hand over a copy of his/her certs upon their departure. I wouldn't honor a welder's cert from another company anyway, because I've seen too many welders "certified" by other companies who's welds couldn't meet minimum D1.1 requirements. It always makes me wonder about the validity of the cert, so I always give prospects a test when they come in to fill out an application. I've also read certs "witnessed" by CWI's such as yourself, where the welder or somebody else used white out and altered their qualifications. One example I remember was that a welder tested with a 3/8" thick plate, but was qualified in unlimited thickness. This is something that you may encounter and have to deal with somewhere down the line, so, always retain a copy of each certification for your records in case someone contacts you with a question.