Are Samsung B-Die and C-Die Compatible?

I am building a NAS (running TrueNAS/FreeNAS) using a SuperMicro A2SDi-8C+-HLN4F motherboard. I ordered 2 sticks of this Samsung C-Die RAM from a supplier but they could only send me 1 as it was the last they had in stock. I ordered the same RAM from another supplier but instead received this Samsung B-Die RAM. I found out this was not a mistake as the C-Die is EOL and the B-Die is its replacement.

While it's not ideal to have two unmatched sticks of RAM in dual-channel mode, the specs according to the datasheets are 99% identical. Do I have anything to be worried about?

These sticks are identical enough that you can freely mix and match them in a server and they should correctly go multi-channel. All of the relevant specs are identical between them.

Virtually everything you will find about the differences will be on Internet forums about overclocking, where it is generally agreed that B-die chips overclock higher and more stably than C-die chips. It's unlikely that you will be doing any overclocking.