I wonder if the P+ poly ones are silicide-block resistors? They can have really good numbers +-10ppm

There are two types of P+ poly resistors, "high res" and "ultra high res". "high res" is 320 ohms/square, and "ultra high res" is 2 kohms/square. There is no reference in the documentation to "silicide block" but I assume that "resistor protect mask" (RPM) is a silicide block mask.