What if I don't change my Master Cylinder on a disc conversion?

Back in 1987 I did a Chevy front disc brake conversion on my 1973 W200 truck. At that time I did not know that disc took a different master than drums. I left the drum master but installed a disc valve. For the next 15 years I 4-wheeled that truck bouncing it all over the place here in the Rockies. I never had any problems or loss of brakes. That being said I look back and feel very lucky. The manufactures had different masters for a reason. These days I always install a disc master when doing the conversion. Masters are cheap and why risk it?