Friend Troubles with Free Trials

My friend has a disk copy of the game from when it first came out but he cant find a free trial with it, So he was wondering if its possible to play on the disk copy until the "Free Trial" of that runs out then is it possible to buy it on steam for the item and free trial and log into the game with the same account and still get the item on this account or would it need to be a brand new account? Is this possible or would it need a brand new charecter/account to get the item and the free trial?

Considering that he will be installing the game from disk just to see if the game has the free trial or not I've asked him to check over the box and it seems just to have the registrations codes inside of it so would it be better of just having him buy the steam game to guarentee a trial (and as a bonus the other expansions) or trying to see if the orginal game he bought has the free trial?

(For TLDR): Could he add the game from steam onto his account and still get the 30 day free trial, item and expansions or would he need a brand new account?

Back in the day, the free trial worked in the following way:

Every user who activated *any* content on PlayOnline *for the first time* would get 1 month free on the first purchase regarding the specific game/product/content. In a manner that if you were to purchase one content for Tetra Master you would get one free month of it. And it was independent of the FFXI content.

You would insert the code on the appropriate page and the free trial would be granted automatically. But you HAD to be in possession of a account with a valid billing source for the trial to enable. And once the trial month ended you would be charged the fraction of the following month on your statement.

So everybody would be billed on the very same day.

Now I can't say how it works as even Square Enix itself is not sure of how it works right now. -_-;

He says he's missing the code, opened a brand new box and the code wasn't inside. I think he's got a version of the game with only the first two expansions as well o O'

EDIT: Ah he says there is a code but it's dotted into the cardboard that the discs were inside (the instructions say that there's meant to be a free trial code but the only codes that are included are the following:

Playonline
Tetra Master
Final Fantasy XI
Rise of the Zilart
Chains of Promathia

Are you meaning to say that if, for example, he was to enter in the code for Final Fantasy XI he'd get a free month of that, but not Tetra Master? Automatically I mean, without having to take any additional measures, the free month would be granted to him providing there was a valid billing source?

Tetra Master is no longer available. It was discontinued in last January. I used it as an example on my post.

And yes, he would get the free trial on the first time he use the code that came on the package.

First code (PlayOnline) was used to create the account.
The Final Fantasy XI code is used to prove you bought the content and is used to enable the content for the game, grant one month of free trial and after that, it was used to purchase new character slots (you can have up to 16) per account.

The last two codes enable the respective "extended contents" they represent. It allows you to play the said contents. They do not grant any sort of free trial.