Thank you for your answer. I'm quite busy these days, which explains my late answer.
What you wrote makes perfect sense and I will adjust my workflow to follow you guidelines. However i get the exactly same problem. No existing specs is updated even though im sure i what is already drawn in the model is drawn with the same spec before catalog update.
Had the same problem, but I believe I know what's happening. When you update the spec, it's updating to the CPak sub-folder but NOT to the Spec Sheets sub-folder in your project. Turn off Plant 3D. Create another sub-folder below Spec Sheets and call it SpecBak, then COPY the two associated files of one of your problem specs into that new sub-folder (this is just a precaution). If you look at the CPak sub-folder, you'll probably find the date is newer. Copy the CPak two associated files into Spec Sheets overwriting the existing ones. Now run Plant 3D. It worked for me. If that works for you now, you can do the same with all the problem specs that won't update. That shouldn't take long.
This is a sort of on topic issue, but I just updated computers and whenever I update specs I do not get the window which I previously did. It's the window which lists all the items which are different from the current specs. It has tick boxes and you can select (through this window) the items which are different.
Does anyone know how to get this back, I have been through the commands list looking for it, but I can't find a thing.