I think the whole deac' issue has come about due to arms being re-activated illegally. Apparently some of the AK's used in the Paris attacks were re-engineered deac's. I think that was a catalyst for this.
( However they would have been older neutralisations. not latest spec).
Anyway if you already know where all the legal firearms are; I suppose some civil servant thought up the idea to log all the neutralised stuff just in case someone decides to have a go at re-engineering it. But that's really not practical.

They'd do a much better job for society if they could get all the criminals to register their firearms!