Even today there are only a couple places in the former Soviet Union that can grow gem-quality synthetic white diamonds. Their production numbers are far less than the output of a single mine, and the results are still rather random. Prior to 2004 or so, the only synthetic diamonds that could be produced commercially were colored and primarily industrial-grade.

Doubtful, for several reasons:

1) Synthetic colorless gem-grade diamonds are difficult to make (they can be produced today, about 2-3 times cheaper than natural diamonds, but in small quantities -- and synthetic industrial-grade diamonds are also quite profitable, with significantly larger and accessible market -- but much easier to create).

2) Synthetic diamonds are relatively easy to identify (with microscope and ultraviolet light source)

3) Even today, Russian-sourced gem grade diamonds are somewhat less diverse in size and quality than their non-Russian counterparts -- and their provenance is well documented.