The question is not about the slightly differing wavelength of the devices caused by manufacturing processes or the shift from changing temperature.
A German source says that the spectral width with which laser diodes emit their light is only 1 nm, in the case of the Distributed Feedback Laser (DFB) it is only 0.1 nm. (“Die spektrale Breite mit der Laserdioden ihr Licht aussenden, beträgt nur 1 nm, im Falle des Distributed Feedback Lasers (DFB) ist sie sogar nur 0,1 nm.“) Could I suppose that a cheap laser pointer has a bandwidth of more than 1 nm?
The bandwidth of a sodium-vapor lamp has two spectral lines very close together at 589.0 and 589.6 nm. This turns out that the bandwidth of this lamp is around 0.6 nm?
For the background see this question about The function of the pinhole in the double slit experiment and therein the comments below the answer.