I believe having a "b" suffix e.g., hx2790b, means the unit has newer
version software (firmware?) or maybe hardware components too, than those
without the suffix, e.g., hx2790.

In units with same suffix, do later serial numbers e.g., 2CL6220..., also
mean they have newer version sofware or newer version h/w components, than
units with earlier SN's e.g., 2CL6180...?