In fact, the same pasted-on cover slick was used for both mono and stereo LPs; but for stereo sleeves the slick was slipped down so that the stereo logo and catalogue number were revealed, rather than being hidden behind the rear cover slick.  And of course, some of the bottom border disappeared round the back instead. 

Some early US "360 Sound" stereo copies actually used the mono sleeve with a stereo sticker covering up the 'eye' logo and serial number on the front and the serial number on the spine.  (Thanks to Andrew Russ for this.)