Oil free is more to do with how it is handled and stored rather than how it was made. Keep away from oil-filled pressure gauges, oiled fittings, bushings, oiled pipes and hoses. Compressed O2 + Oil, or oil + liquid O2 = explosion.
We never certified O2, N2 as sterile.
Probably the most important test you could do on O2 med, or breathing air would be for CO content.
We did smoke test for N2 purity against O2 content.
Dew points for all.
The biggest difference was that industrial O2 went into red bottles, med into green.
Learn from the mistakes of others. You don't have time to make them all yourself.