Para quien necesite referencias, aquí varias páginas de las mismas:
Just so there is no confusion as to what is and is not unrestricted stock here is the definition in LawrenceDeDarks own words.
"Unrestricted stock can be used for both personal and commercial projects, but it cannot be redistributed as stock. You are not required to obtain permission prior to using the stock off site or in DA prints. The only requirements are that the stock provider be notified and credited."
This is the basic rule,. However some stockers may have some requests such as how to notify them of stock use and no using stock in pornographic, derogatory, antireligious or in ways that might be considered illegal either in their own country or the user's. I don't think this is unreasonable so do make sure to check out the individual's terms of service.
This list is subject to change as I find more stock providers or artists close or change their terms of service