If I already purchased a Chinese Visa but am planning to enter through Nepal will my visa be good?

I purchased a multi- six month one for China through the Los Angeles Embassy using a travel agency here in Las Vegas. I was planning to fly into Katmandu and then take a tour group from Katmandu through Tibet. After the 9 day tour I was planning to fly to Beijing and visit that area and Shanghai area until my flight back (about a total of 30 days). I read that if I have a L type and then get a group one that it will void my L type. Is this true and what would you suggest to be the best way to have everything I need prepared for my trip?