I have already got Logos 7 Platinum base package and LN, do I still need Logos 7 Basic which is offered for free?
You already have the latest version of Logos. Logos 7 Basic is mostly intended to (get people to try out Logos or) get customers to upgrade from an earlier version of Logos.
But, Logos 7 Basic happens to also give you access to one resource that isn't in Logos 7 Platinum (likely because the paid base packages have better lexicons).
So while you don't need it, it's really a question whether or not you want access to that particular resource.
Thanks to FL for including Carta and a Hebrew audio bible in Logos 9!
Tony Lim: I have already got Logos 7 Platinum base package and LN, do I still need Logos 7 Basic which is offered for free?
You don't need it but you may get access to one additional resource - https://www.logos.com/product/41596/a-pocket-lexicon-to-the-greek-new-testament - which isn't included in other base packages (though it is in various bundles)
Also, will this Logos 7 Basic be added into my current existing Base Package or it function as a separate software?
Tony Lim: Also, will this Logos 7 Basic be added into my current existing Base Package or it function as a separate software?
If you use the same username and password, it will be added to your account. There is no separate software... it is the same software.
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You may also want to check out a recent article on the Logos Blog, "Should I Get Logos 7 Basic If I Already Own Logos?".