I don’t see what all the fuss is about. There are rumours and then there are red herrings.
I haven’t checked the MSNs but the A321 can have one Additional Centre Tank (ACT) giving 20.9t FOB, two ACTs or no ACTs. Just because they are there doesn’t mean you have to use them. In fact they impinge on cargo capacity so would only be fitted if routinely needed. I wouldn’t get stressed.
A310, A319, A320, A321 and A340s may be fitted with ACTs.
Until they takeoff with you on board it hasn’t happened.