LED strip does not have SMD Resistors
Looks like they have thick-film printed resistive material (ink) rather than installing SMT resistors. That's what those black rectangles are. A way to make it a bit cheaper and crappier. One resistor for 3 LEDs is correct for 12V. It's probably the same FPC layout as for resistors.
If you measure the resistance from end-to-end of one of the rectangles (vertically in your photo) you should be able to measure them. Probably somewhere in the 100\$\Omega\$ range.