Found this great resource which actually lists every City transfer right into the dim and distant past.
https://www.transfermarkt.co.uk/coventry-city/alletransfers/verein/990
I can't attest to it's accuracy but it looks OK.
When it comes to losing our best players to bigger clubs my experience has been honed over many years, I remember Carr, Mortimer, Lloyd, Dublin, Boateng, Gillespie, Speedie, Babb, Kirkland, Pearce, Wallace, Ferguson and Hutchison all going.