If they really have 500 million ounces of silver, then yes the stock to be $50+ in two years. However, only about 10% of that figure is "measured and indicated" bur rather "inferred". That's why the El Quevar updated resource estimate is key. The more silver they can prove the more the share price will be rewarded.
That's why I'm so f'in annoyed at the delays in releasing the resource update. In mid November both the El Quevar and Velardena resource reports were expected by the end of the year. On 12/8 they pushed out the Velardena report until late Q1 and said the El Quevar update would come out "about year-end". It could be released any day now and if they substantially increase the the "measured and indicated" figure the stock could double in 1-2 months. I do admit to owning some Jan $7.50 calls which is making me display my impatience. :-)