It is VERY confusing...
There is the original Gold Bug, from many years ago...not at all similar in appearance to today's "Gold Bugs." Then, there was the Gold Bug 2...this is a gold prospecting machine, running at super-high frequency, and again, bears no outward resemblance at all to today's "Gold Bugs."
Then, a few years back they released the Gold Bug Pro. There are several early versions floating around, some with minor differences to today's units. One older unit that is fairly common is the "2.9" version of the unit (software), which is different in some small ways to the current Gold Bug Pro. There have been software updates since the "2.9" version, my version is "4" and there may be a "5" out, as well. Anyway, the Gold Bug DP is another of these units, and is EXACTLY the same as the Gold Bug Pro, except that it comes stock with the 11" coil, vs. the 5". Then, there's the G2...it comes, like the Gold Bug DP, with the 11" coil as its stock coil. The only difference between the G2, and the Gold Bug Pro/DP, is the rod configuration. Software-wise (and thus performance-wise), they are the same. Then, finally there's the current edition of "Gold Bug," which is sold, for instance, in at least one of the big national sporting goods stores. This unit is VERY similar to the Gold Bug Pro; in fact, I'd be willing to bet that it is nearly identical, but simply costs less so as to be more competitive, price-wise. I have not used one of those units, so I cannot say what, if any, minor differences there would be between it, and the Gold Bug Pro, but I suspect there are a probably a few very minor ones. Someone else here may know, but otherwise, I hope the info I have given helps you out some.
Steve