At almost no stage does the bagpipe music we hear on the soundtrack match the pipers' fingering we see. In addition, during the band practice scene the band goes from being in step with the music (first beat of the bar on the left foot) to out of step to back in step again.
Pipe Major MacLean is never shown with a set of bagpipes. In particular, he is a mere observer at band practice. A pipe major is not only the leader of the band but also its chief instructor, and it is unthinkable that he would not play an active role in all practices.
Major Sinclair starts the first day of Colonel Barrow's command still wearing his previous acting Colonel rank. Half way through the day (between the assault course and watching the pipers), his rank changes to Major. Whilst it is possible he might have had his jacket altered over between the scenes, it is not possible that Colonel Barrow (a stickler for uniform regulations) would not have mentioned this at the start of the day.
The goof item below may give away important plot points.
Boom mic visible
When the gunshot is heard while Major Jock Sinclair and friends are in the snooker room, the camera pulls back as they slowly turn; the shadow of the boom mic is seen over their heads on the wall behind them.