Council tax payments and HMOs / illegal conversions

I have done a bit of snooping around online, as I do. What I found is puzzling me.
The HMO opposite me was down in this register of council tax bands as "deleted": http://www.voa.gov.uk/council_tax/cti_home.htm
All 4 flats were down as deleted.

I called the council tax office to enquire about this. They informed me that the house was down as a band "E", which is normally the band applied to a whole Ladder house, used as one residence, so should not apply to flat conversions. From what I can gather, flats are down as band C.
As this particular house is 4 flats, I assumed it was a band B (I'm guessing here).

From what I can see, the relevant council tax should be 4 x rates for, let's say band B for argument's sake.
To compare, band E is £1798.37. That's usually for one whole house. A band B flat is £1144.49, so total for that house should surely be that x 4 = £4577.96?
It looks to me as if someone is cheating the council out of A LOT of council tax.

Have I gotten this completely wrong, or is this yet another case of the council not knowing it's backside from it's elbow again? If the lack of communication is this severe then I am wondering how many £££££ they're missing out on in council tax payments, and also how many illegal HMOs are getting away with paying far less than they should. This seemingliy because the planning office does not communicate with the council tax office.

I have emailed the council tax office about it - but it seems like another case of the coucil not coming what the rest of the council does. I'll let you know when I hear back.

It might be worth looking into this for other illegal conversions you are aware of on your own roads.