Recently Expired prep still good?

[miticax]

Had a bottle of prep that expired last month, and I do on demand prep rarely. The bottle was opened 3-4 months ago but stored at least in a dark place (although not necessarily cold)
Is this still good for another on demand play or better just throw it away?

[viking8x6]

It should be fine if it wasn't exposed much to hot or humid conditions (temperature >30C, humidity >80%RH).