The "Stock Block" line is used to identify the batch of stock reported on Form 7203. The description is not important to the IRS, so use something that is useful to you - number of shares, date of purchase, etc.
Part I Line 1 is the stock basis from your prior year return. Your original basis is your cost to acquire the stock and doesn't reflect the market value of the stock.
Line 15 represents your ending stock basis, which will factor into the calculation of taxable gain or loss when you sell the stock. Otherwise, the calculations on Form 7203 are used to track the various transactions that increase or decrease your stock basis. Since these transactions have been reported to you on Schedule K-1 since you first purchased the stock, Form 7203 has no effect on your current tax return.
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