Where did you hear Adrian Smith replaced Dennis' parts?
The Tony Platt sessions on 16-18/10/1980 were the only known sessions for "Women in Uniform" w/ Stratton in the band. When Adrian joined Maiden he went straight into rehearsals in Clapton for the last part of the tour. At the same time Maiden released the german version of the EP. I have this note:
03/11/1980 - A new “Women In Uniform” EP version is out under “Special Live Ep” title, in Germany. EMI Electrola label.
This 1980 special EP has the same cover artwork as Iron Maiden LP and it probably contains the 2nd mix (as it happened with a few other german singles), being the reason it was called "German mix". I'm not sure, so please check its version!
This mix is an alt. mix without the other rhythm guitar in the beginning of the song. That's the main difference. I don't particularly hear any guitar differences in any other part (which would be the case if Adrian played in it).
Anyway, I've emailed Tony Platt about the subject. He heard the mix and said this:
I’m not at all sure whether this version is a remix but it certainly isn’t a re-recording. The suggestion that Steve Harris mixed the original version is also nonsense - I was at the mastering for the releases so I know my mixes were used.