Since your 1099-B has all the info for you, you could enter the latest vesting date of 3/10/18 as 'date purchased'' and make one entry. This makes the sale reported as Long-Term gains/loss for you.
The X in Box 5 means the broker doesn't know the purchase date, and you want to be able to indicate 'Long Term' for your sale.
It could be problematic entering four separate sales, not only because it doesn't match the 1099-B but because some shares were sold for taxes. The total shares of the four lots won't match the total shares sold on the 1099-B and you probably don't know which lots had shares sold for taxes. If you do have that information, you could enter each lot as a separate sale.
If the four lots had different Cost Basis amounts, you can compute an 'average' to enter as Cost Basis, since your 1099-B probably has $0 as Cost Basis. If it does actually have a Cost Basis, great!
Remember, the cost basis is the Fair Market Value on the date the RSUs vest.
The most important things about reporting a stock sale are the 'date purchased' (for the long/short determination), and the correct Cost Basis (so you don't over-report your income on the sale).
Here's more discussion on RSU Sales.
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