Exactly correct. GW letters are a leap of faith that a human being on the receiving end will take pity on you. I used the address listed on my CRs. Began the letter Dear Madam or Sir.
However, there is growing opinion over on CIC that GW letters work better when sent to executives, and even Email. I tried it with Target after two GW letters yielded not a word in response. No luck yet. And no luck with GW from AMEX either, but that TL went to collection.
But the risk is nil, rewards are high, and the odds are better than Vega$.
GW is best for lates, particularly old lates, but use it for any lates--whether the account is open or closed.
I have yet to hear of anyone getting a paid collection or paid chargeoff deleted via GW, but it's probably happened.
If you still owe the OC money, GW may or may not work. One of my Chase GW deletes was on an account that was settled for less than the full amount. I guess my advice would be if you've paid the OC most of what you owed, then give GW a try. IIRC, the Chase account was for about $1700 and was settled for around $1200.