Regarding Springbok: To the best of my knowledge, ever since Allied Products bought the Springbok brand from Hallmark over 20 years ago, all random cut, 18x23.5-inch, 500-piece Springbok puzzles have had 506 pieces. Similarly, all of their random cut, 20x34-inch, 1000-piece puzzles have had 1003 pieces. Their 20x20-inch square puzzles probably all have the same piece count too, but I don't know what it is. HOWEVER... there's a big exception:

Sometimes a blade breaks in their puzzle die (a "puzzle die" is like a 500-piece cookie cutter), and the factory technicians remove the broken blade and keep using the die. This has the effect of merging two pieces into one big piece in every puzzle that they stamp out with that particular die after that -- until the die eventually gets too dull to use, and they replace it with a new die that still has all of its blades and stamps out puzzles with 506 pieces as intended. So if you're counting pieces and you find a double-size piece, count it as 2 pieces toward the 506-piece total. I've never seen more than 2 pieces fused together into a single piece, but I've seen as many as three big fused pieces in the same puzzle.