Aside from all the other issues that have already been discussed in this thread, why would anyone expect to see a +P rating on a revolver that was made before +P ammo was on the market? You didn't identify your Model 36 by serial number, but there is a good chance it was made before anyone was marketing the so-called +P cartridges.
Jack
Added: I just looked again at your photo and it may be that your cylinder release has the angle cut on the top. If so, my comments do not apply to your gun, but I see this question stated this way a lot, referring to guns made in the '60s and '70s. It makes no sense.