MAN-JNB availability on Expert Flyer reliable?

[polb]

I booked 4 reward seats in business MAN-JNB for July 2024 on the day they were released. I need another 2 seats as there are 6 of us travelling, but based on availability last year I thought I’d wait to see if any more were released in business and if not I would pay cash, business if the price was right, if not premium or economy. I’ve been checking expert flyer and it’s been showing the flight as sold out in all fare fare buckets except expensive bussiness, for a few weeks now. Does anyone with more knowledge than me have any suggestions to why this would be, surely the flight isn’t really completely sold out in economy already?  I’ve checked several days either side of our date of travel and they’re all showing the same thing. Maybe I’m not reading the info correctly. 
​​​​​​​TIA

[Deek]

On seatspy I see availability almost every day in July in economy & prem economy from LHR-JNB, and 1 business seat on 11 July. Maybe it’s the MAN-LHR throwing you out?

[e14]

It will be a married segment availability MAN-LHR-JNB – you will probably be able to see MAN-LHR and LHR-JNB if you put them in separately.
If the married segment low fare (I class for business) is sold out then it is unlikely to come back unless there is an aircraft swap

Check to see if EDI, NCL, BHD are also sold out.