WD Red 8Tb Why are some helium and some not?

I have four 8tb WD Red drives bought at different times.

I had to RMA one and the one they sent me back is a helium drive. This runs a lot cooler than the others and I’m wondering why two drives both labelled “WD Red WD80EFAX” are so different?

It’s not like the manufacturing process has improved over time and helium become unnecessary because the helium drive was manufactured after the non helium ones.

So why are different drives, with the same model, built so very differently?

Hi Tom-B,

You can refer to the link mentioned below to know more about WD Drives.

https://support-en.wd.com/app/answers/detail/a_id/19814