Questions about PHS-memory RAM suitable for Synology DiskStation DS1522+

Hi, I have a brand new 1522+ and an 1821+ with 2x4GB of RAM. More than two years ago, I replaced a 4GB strip with a 32GB DDR4 2666 ECC strip from Micron. It worked perfectly, with no Syno error messages. So I got an original strip from the 1821+ which I tried on the 1522+, did a memory test with Synology Assistant, and it worked without a hitch or error message. Am I to conclude that the memory in the two Synos is exactly the same? If so, would the PHS for the 1522 also be compatible with the 1821+? Thanks for your advice.

They write that this 32GB memory is 100% compatible for Synology DiskStation DS1522+ and it says 1 unit. According to Synology, the maximum RAM for the DS1522+ is 32GB in two times 16GB units. How should I understand this Ram? Is it possible to install 2x 32GB Ram? Does the 32GB come in 2*16GB and is the unit count wrong with 1 unit? Thanks for the clarification.