It was indeed that issue you’re thinking of back in the day that enabled CS to redeem digital TBC CE online after a simple method & check.
The problem was that these continued to be redeemed way beyond the amount of sold copies so they stopped. Mainly because of nefarious individuals re-selling them.
Then after public protests on the forums they revised their policies and declared all players who redeemed TBC CE’s will have to submit several physical parts of their CE’s forever removing them from the circulation.