First, I don’t know what you mean by „historical data beyond 1989” and how you reached this conclusion. And I don’t know what do you want to day by the Chamber of Commerce. This is about legislation, not trade.
The portal contains the entire legislation that is applicable today but not legislation that was revoked.
For example, it does contain the agreement between the Socialist Republic of Romania and the Republic of Turkey, which is still valid: http://legislatie.just.ro/Public/DetaliiDocument/45731 (probably the Chamber of Commerce can confirm). But it does not include the Constitution of the Socialist Republic of Romania, which was repealed.
Second, if you read the terms of the website carefully (see: http://legislatie.just.ro/Public/Termeni), you will likely notice in the last paragraph that the legislation is not protected by copyright and the content of the website can be re-used freely. There is indeed a disclaimer saying that the content can not be used, for example, in Court, because by law only the Official Gazette is providing the legal reference. But this is a different story.
And finally, the content can be downloaded in bulk via API, using the instructions available here: http://legislatie.just.ro/ServiciulWebLegislatie.htm. However, there is no link to download the whole database directly from the browser but I guess that it is because technical reasons.