We don't have a need for it to appear as a variable but we also want to have the number as a reference if needed. We found the easiest thing was to type the number (it's short) into the comment section when doing a transition. This would then appear in the history.
We like to have at least the most recent revision number and name on all of our drawings, so having it auto populate as a variable rather than manually going to each drawing and entering it would be helpful. If there is no way to apply the variable in the ECN to all of the parts/drawings it contains I may look into having people enter the ECN number and name in a specific format as a comment then trying to parse the comment into the two variables. I'm not sure if that is possible either.
I have thought about doing this too. I can't wrap my head around it totally, but here's what I was thinking:
Create an ECN folder. Have folder card variables with the EC information.
Move all effected files into that folder.
When you do the transition to start the ECN process, roll the ECN number/descriptions/dates to the next set of ECN variables (we have 3 sets on the drawings), then populate the ECN information though the transition pulling the info from the folder card variables... Name your transitions for the EC document and the parts/assemblies/drawings the same. That way it you can transition all of them at the same time.
Once the EC is complete, move all the files back to production folder.
I might be way off, but I haven't put too much thought into it lately.
I was trying to do the same thing for something very similar. My solution wasn't to read a variable from the ECN and apply it to the other files, but to use a dispatch script that triggered before the transition. The dispatch script first prompted the user for the ECN number (before the all documents block start), then applied it to all the documents (after the block start). The image below shows this better than I can explain...
It's not as great as reading the value from one file an applying to others, but it is the next best thing.
I hope this helps.