I can only speak about the Max length of storage of barley in order to maintain malting quality. With your storage conditions.
75 F @ 10% moisture = a kernel with even germination potential, will last for 1 year. Malt is <5 percent, maybe it will work.
If you have access to a moisture meter get a reading. Insure you have no insect infestation.
I would be hesitant to do full batches with this malt, why not blend it with fresher malt. a 10-15% ratio until it is gone. Send some samples.
Rebel Malting Co.
Reno, Nevada USA