Unfortunately upgrading to the latest version of Nitro didn't resolve the issue, nor did a few other things we tried. So I was pretty-much forced by the client to troubleshoot this further because Nitro is rather important to them as it's used to combine .pdf's, e.g., upon printing from Sage they often will select an existing .pdf which gives them the option to append to that .pdf. I'm not aware of what other .pdf creator programs have the same functionality, but I got the sense the client didn't want hear about it anyway.
So upon further troubleshooting I ran into some serious inconsistencies between what forms did and didn't successfully .pdf on one computer vs. another. _**The resolution in the end appeared to be to set the forms with ""no printer"" inside each Crystal form, and then additionally on one of the computers I changed the default Windows printer to a regular laser printer (it was set to a non-standard printer; label printer I think).**_ Now all seems to be working.