This is a great question. The answer is that primer flattening and flow are not useful indicators for assessing chamber pressure in low pressure rounds like .45-70 and .30-30. These changes occur at a given pressure that's independent of which cartridge you're using. For example, if primers flow at 70,000 psi, that's too high a pressure for a .30-06, but a good rifle would probably contain it. A trapdoor Springfield in .45-70 would surely blow up before reaching that pressure. The bottom line is that you can't take the absence of these primer signs as an indication that your load is OK. Another factor is that different primer brands have different degrees of cup hardness, which affects the pressure at which these signs appear.

This has been discussed before with regard to handgun cartridges. A good example would be the .44 Special, which has a SAAMI maximum pressure of around 15,000 psi. If your load developed 25,000 psi, you'd have no way of knowing it from primer condition. Such a load might be OK in a modern N-frame S&W, but I sure wouldn't want to use it in a Triple Lock with its non-hardened steel cylinder.

Flattened primers, especially with Federal primers, occur routinely in Magnum handgun cartridges and are not necessarily a sign of high pressure.