Some time back I purchased all of the Dupont Cronor materials necessary to paint a Z-28. I sold that project and moved on to another before the paint was applied. I live in north central Texas where the summer temperature lives near 100. The materials have never been opened and have been on a shelf in my garage for a few years.

Is it still suitable for use?

I have a live in North central TX and paint will not last.
Maybe if your lucky, stir it up real good then see how it looks.
I have had paints that did not last long, but I have also had some last for a while. A few years may be too long.