This isn't correct. Production costs must be subtracted to calculate surplus value.

Surplus value is "worker value added". To get worker value added, you must subtract out the cost of materials, etc.

In the USSR, there was no surplus value whatsoever; any "surplus" consisted solely of taxes earmarked for social benefits and similar expenditures.

This is also incorrect. Socialism and the USSR has / had a surplus, its just that its directed and controlled by working-class political decision-making, and not by private capitalists. It may direct that surplus into defense, research, social services, etc. It has a different form than capitalist surplus value.

Here's some vids on this:

• https://www.youtube.com/watch?v=C-T-Fr6DvFw
• https://www.youtube.com/watch?v=Nu85byBBddY