[dom0]

Well that's stretching the meaning of second sourcing quite a lot. Normally it means that you can get an exact replacement part from someone else. For example, industry standard things like nuts, bolts, ball bearings, SRAM and DRAM (most stuff specced by JEDEC) can be sourced from many sources. There is literally no difference at all between a M8×20 8.8 bolt between manufacturer A and B. Similarly, if you have a design with a LM358 (a non-standardised part), then there are multiple manufacturers that will sell you a part with identical specs under a slightly different name or even the same name.

This is also the way it started with x86 and other second-sourceable processors. An Intel 8086 and an AMD 8086 are drop-in compatible. This is not the case with modern processors, they don't even fit the same sockets.

[temac]

But you can change a larger module. If you want to cover that kind of risk with that kind of supplier companies (hint: a marginal risk, to begin with), you are not going to go anal about the drop it characteristics of single chips. Or at least you should not, IMO.