The 17th Edition is really just the 16th Edition with all of the interim updates included. AASHTO wanted to publish one last "clean" version of Standard Specifications before they archived it and moved on to the LRFD Specifications as the new standard.
If you have most/all of the interims for the 16th Edition then your copy will be fairly close to the 17th Edition (with a few subtle changes). Even without the interims, you may still be OK, but you are taking a small risk.
My experience has been that the Bridge questions on the PE exam are fairly basic (retaining walls, distribution factors, impact equation...that sort of thing). Chances are very good that your copy will work for the basic questions that you are likely to see.