All Airworthiness Directives are mandatory.
No, this does not represent a fleet-wide corrosion problem with the CJ series.
The AD requires simply requires an inspection for corrosion and disabling the relief tube, and if corrosion is found (which would be caused by use of the relief tube) to repair the corrosion by necessary means up to and including skin replacement and application of a corrosion sealant.
If the relief tube was never or very rarely used, then it'd be safe to say the odds of finding corrosion during the inspection are minimal.