If, by “deductions,” you mean payments from the customer that have been credited against the sales invoice, the standard version shows the total amount credited and remaining balance due. But the standard sales invoice is not written in HTML.
On the other hand, if you are referring to a custom view template you have created, what it shows is entirely up to you. In this case, you should be aware that the sample HTML code that appears when you begin creating a new view template is not the code for the standard invoice. It is only an illustration and lacks many features of the standard invoice, including the ones mentioned.
This has nothing to do with reliability or power of the software.