I will try to clarify the points made by you:

a) Restricted access has to do with restrictions to who can obtain access to your database. First of all, access would need to be on subscription basis. In addition, you would need to make the case, that your audience is not the general public, but a specific user group.

b) Your Site License subscription gives you dowload access to all UN Comtrade records. Data are made available to you for internal use. The Site License subscription is valid for one year.

c) If you obtain the right for re-dissemination of 20 million records, this means that during a period of 12 months you can make up to 20 million records available on your website. We are not counting how many records are downloaded from your website. Only the number of records made available on your website are of concern for the re-dissemination fee.

d) Suppose that you make 18 million records available on your website during the 12 month period. These 18 million records can stay on your website after the 12 month period and you would not have to pay any additional fee. However, if you make new data available in the period following the first 12 months, then you need again to obtain the right to re-disseminate UN Comtrade data.

UN Comtrade does not include Tariff information. Tariff information can be obtained from the TRAINS database (see http://r0.unctad.org/trains/) which is nicely integrated in to the WITS software (see http://wits.worldbank.org/witsweb/default.aspx), which also contains Comtrade. For access to Comtrade data via WITS, you will need a subscription to UN Comtrade data.