The figures suggest that losing a bag on BA is extremely rare, and that delayed baggage is also very rare too. So you have been very unlucky (and I write as someone who never checks in a bag). The numbers are something like a below 1% chance of delayed luggage (under 1 to 10 bags per 1000 passengers, depending who does the figure collection) and lost baggage is less than 5% of that. Generally airlines are improving their act in this area, due to better technology, and BA is investigating RFID chips as part of its efforts. The two things that get in the way of a good news story are connections - far greater risk of problems arising from that - and bad weather/mechanical snafus.

As for following up / chasing up bags, personally I wouldn't try too hard. The airline will reunite you with the bag at some point. The exception being that sometimes a bag will turf up at a middle sized location and they seem to be unsure what to do, particularly if BA don't actually fly there. So it sits behind a ground transportation agency desk for a few days until someone gets around to dealing with it. A well timed telephone call will at least give you the option to collect the bag. Otherwise buy what you absolutely need and charge it to BA.

It would be tempting to think airlines prioritise reuniting you with your bag, and will be constantly monitoring its progress and making it the focus of their attention. Well that's not the way it works - it gets batch treatment and every so often the batch's status gets an update. Frustrating? Certainly, but that's the way it works.