A lot falls under the category of 'stainless'
The non magnetic stainless (high nickel content) is the most corrosion resistant 304 etc used in halfway decent flatware, 316 etc (often used in better watches etc) is about the best for general use. You can recognize nickel bearing (austentitic) SST because it is non magnatic.
Unfortunately it does not weld easily, and is hard to fabricate. There are martensitic stainless which can be very hard (used for sst knives) and it is magnetic.
There is also ferritic sst, which is easier to fabricate and weld, less corrosion resistant.
But there other issues, which I suspect at the base of your problem. Welding can seriously damage the corrosion reisitance of SST, and must be done with special precautions. Boat builders know this, but perhaps shortcuts were taken here.
Additionally carbon steel in close extended contact with sst (such as using a carbon steel bolt) will actually start the SST corroding as the carbon particles migrate across the boundary.
Your best bet at this time is to throroughly clean all rust spots off, and be cautious about steel to sst contact.
If the welds do rust, I'd see about what the mfgr will do for you.