Originally Posted by Grand Union

Award tickets and MFU’s (Miles for Upgrade) on BA book into one of four fare buckets, X for Economy, P for WT+, U for Club, and Z for First. The amount of seats left in each bucket is only viewable to BA. It isn’t made public on GDS’s such as Amadeus and Sabre – you cannot search for them on ‘availability tools’ (like ExpertFlyer or KVS). To check availability, you can either call them and ask (they’re usually very obliging), or just check yourself on ba.com – this shows the same availability as BA can see themselves.