The problem arises when you have players who span different decades ( which is most of them)
Colin Jackson for instance, over 500 games but 3 different decades
Correct but the question asked was for each decade, below is a list of the top 25 all time appearances in all competitions played in.
The list heading is Player, Total App, Starts, Subs and Goals
Dougie Gray - 888 - 888 - 0 - 2
John Greig - 777 - 773 - 4 - 124
Sandy Jardine - 695 - 667 - 28 - 84
George Lewis Young - 663 - 663 - 0 - 62
Sandy Archibald - 652 - 652 - 0 - 166
Davie Meiklejohn - 632 - 632 - 0 - 52
Alec Smith - 610 - 610 - 0 - 195
Ian McColl - 594 - 594 - 0 - 17
Ally McCoist - 585 - 503 - 82 - 362
Jock Shaw - 584 - 584 - 0 - 4
Willie Waddell - 569 - 569 - 0 - 148
Derek Johnstone - 561 - 537 - 24 - 208
Davie Cooper - 552 - 474 - 78 - 79
Peter McCloy - 550 - 550 - 0 - 0
Colin Jackson - 527 - 524 - 3 - 41
Alex MacDonald - 521 - 495 - 26 - 99
Jerry Dawson - 514 - 514 - 0 - 0
Willie Woodburn - 504 - 504 - 0 - 2
Alan Morton - 494 - 494 - 0 - 117
Tommy Cairns - 489 - 489 - 0 - 157
Ronnie McKinnon - 488 - 488 - 0 - 4