Respectfully, I believe you are off, but wouldn't say "way" off though. Reading other WR salaries, I just don't see how a team pays Randall Cobb $9 million a year, UNLESS it is back-loaded similar to how Nelson's contract is. It's easy to pay a player $10 a year over 5 years and still only have a $5 million cap hit in year one and escalate throughout.
I think Packers gave Nelson a 3 year $13 million contract after his rookie contract. I do think Cobb will get something more favorable to his liking. Nelson was the 2 at that time, just as Cobb is now.
Here's what left for Nelson.
Year Base Salary Signing Bonus Roster Bonus Workout Bonus Cap Hit Dead Cap
2014 $2,000,000 $3,175,000 $500,000 $250,000 $5,925,000 $11,750,000
2015 $1,300,000 $2,300,000 $500,000 $500,000 $4,600,000 $9,200,000
2016 $5,500,000 $2,300,000 $500,000 $500,000 $8,800,000 $6,900,000
2017 $8,250,000 $2,300,000 $500,000 $500,000 $11,550,000 $4,600,000
2018 $9,250,000 $2,300,000 $500,000 $500,000 $12,550,000 $2,300,000
Cobb being 23 (24 in August if you want to give presents) I wouldn't sign anything more than 4 year deal and preferably a 3 year deal. If he proves consistent the next three seasons, he'll be in the middle of his prime and the salary cap will be even higher and he'll be able to really cash in.