I was the victim on the exact same model being smaller than the older one. I was trying to save money by buying used drives from GoHardDrive. One of them started throwing SMART errors. So I figured I would be wise and buy the exact same model drives. That ended up not working out as the new 12 TB drives were like 1.2 GB smaller than the older exact same model 12 TB drives. I bought 4 in December and five in February. All five February drives were 1.2 GB smaller than the December purchased drives. Same model from the same vendor.
The same thing happened to my NVMEs. I had two 1 TB NVMEs from different manufactures, one well know brand the other not so much. The two were 100 MB or so different and TrueNAS was giving an error. So I ended up buying another of the more well known brand to get rid of the error.
In any case, I ended up buying four brand new 14 TB drives, so my desire to try to save money with GoHardDrive was foiled. So $500 in drives before and over $1000 in drives now because I can’t guarantee a 12 TB drive is a 12 TB drive according to TrueNAS.
In the meantime, if TruNAS were to put that swap partition in, it could make it so every drive nominally the same size is the same size that TrueNAS can use.