Your first set of numbers quoted ("High grade previously") is based off a 2.0% Pb cut off grade - as per slide 15 in the investor presentation released 25 Jan this year.
The second set of numbers you're comparing it to are the indicated resource numbers released in this mornings announcement and these are based off a 0.5% Pb cut off grade.
You need to compare numbers based off the same cut off grades.
MYL Price at posting:
5.5¢ Sentiment: Hold Disclosure: Held