Another great idea introduced by JAA, on the old CAA system an upgrade test was required to go from AFI to QFI (the equivalent of FI(R) to FI).
As mentioned it is quite common at some schools for an FI to "hand" over solo sign offs to an FI(R), hence it is possible for someone at get the signs off quite quickly, even though they may have only flown one circuit with the student (the point I assume VFE was making).
Also you can get FI (R) whom may pick up students in the latter part of the PPL course, hence it is then very easy to keep sending the same student solo on continuous days. Therefore the 25 solo signs are quite meaningless as a measure of instructional ability.