Is there a reason why you're creating STEP files from NX and importing them back into NX? Other than checking the translation results (which as you have already seen isn't 100% accurate for checking how it will behave in other CAD softwares), that seems like a long way around opening an NX file directly or using a Parasolid export. Based on what you're describing, that's the way I'd test it out & see what happens. Your surface bodies aren't going to automatically be added to the PART reference set (I think that's what you mean by 'final part reference set') and in order for the translation to show those bodies (in NX at least) you're probably going to have to either add them in the source NX file OR after opening or importing the STEP change your reference set to Entire Part.

So the issue becomes clearer now that all details are given. NX 10.0.2.6 RE: NX 10 - Hidden bodies after STP conversion Xwheelguy (Automotive) 11 Nov 16 17:53 Hidden symbols and 'anomalies' discovered in 800-year-old 'Stone of Destiny' to be. The reference set was my first try, while I've pressed all parts into the final part reference set, then the STEP file did not contain hidden bodies by default. Photos have been circulating that show bodies being unearthed beneath the famous Easter Island head statues. I see no difference between opening file by importing and opening (issue is still). Sometimes, when the model is easy, the representation could be 'Entire Part'. The models are done by surface design and for the representation on the assemblies, I use reference set that contains only the last detailed solid body.

Then in the Part Navigator there are some bodies hidden by default. When I'm done with STEP transition, I open the STEP file once more in NX. Indeed, sorry my mistake - the parts are not hidden in Assembly navigator (instead of Part Navigator). To make it completely clean: I export selected objects (by clicking on them) to the STEP file, they are not hidden while I'm selecting them.