Yeah I wish they were all sealed. It's strange how they alternated the eyes they used. I assume they just went with whatever they found cheapest but you'd think the sealed eyes would always be more expensive.
Sealed CdS eyes were an option many photocontrol manufacturers offered back in the days of electromagnetic photocontrols instead of the standard CdS eye. There was probably an added cost to them though. It's called "hermetically sealed". Like how today, you have the option of CdS eyes, or silicon for electronic photocontrols.