Explanation:
An alternative, that has the advantage of being 100% accurate, as opposed to "post-approval" which is 99.9% accurate.
There is no reason to depart from the literal translation. It conceivable that there could be an approval which was not followed immediately by registration, e.g. because the investors themselves demanded more data.
When you get outside the U.S. and U.K., Russia not excluded, it is hard to guess what English terminology the country prefers.
Note: If the author wanted to say "post-approval" he easily could have done so. E.g. исследования после утверждения.
---
Regulation of drug use and post-registration surveillance - Elsevier
by PA Phillips-Howard - 1994 - Cited by 6 - Related articles
Post-registration surveillance is needed to monitor, at country level, ...
linkinghub.elsevier.com/retrieve/pii/0035920394904782 - Similar