How much discount for 30th anniversary?

The DIY store chain who has often been annoying enough with its frequent advertisements “20% on everything – except pet food” – whatsitsname again, erm, yes, “Praktiker” (=practitioner) – apparently now celebrates its 30th birthday. But not that they’d just say “30% on everything” now, oh no, according to today’s flysheet:

• 31% on cair conditioners and fans,
• 27% on tiles,
• 24% on furniture and racks,
• 23% on building elements,
• 22% on fireplaces and heaters,
• 21% on wood.

All that from Feb 1 to 4; plus from Feb 5 to 7:

• 33% on all energy-saving lamps.

That raises some questions for me:

• Did they price these things so tightly that this is the maximum discount they can afford?
  
• Or are they just trying to pretend that were the case?
• Did they roll the dice for these numbers?
• What can we expect the next weeks and months?
• Is it worth the potential confusion of customers and employees?
• On average (with regard to their total sales volume), is that more or less than “20% on everything”?
• Are these the next lotto numbers?

(Note: More or less regular updates of current rebates in German.)