If it's an OEM version, the desiccant material will be XH-5 and not compatible with HFC134a. Since you're using R12, that concern is off the table.
A new unit left open to the atmosphere will also be exposed to ambient contaminants such as dust, soot, ozone, and other gases, none of which will be good. If the descicant bag deteriorated, that material will circulate in the system and be difficult to cleanse.
I once tried to reuse a drier. I pulled a vacuum and even warmed up the cylinder with a heat gun. I still got the black death coming out of it.
Today, I would have the receiver-drier cleaned & refurbished with new desiccant. I believe
Classic Auto Air performs that service but the lead time is very long. I've got four of my driers waiting for it.