To expand, a while back, I went through HSP and tried to account for all of Gretzky's points that year with his teammates.
EVSG: amount of player X's goals that Gretzky assisted on at even strength
EVSA: amount of Gretzky's goals that player X assisted on at even strength
AEVSA: amount of Gretzky's assists that Player X assisted on at even strength
Same legend applies to powerplay and shorthanded points.
Player X| EVSG | EVSA | AEVSA | PPG |PPA|APPA|SHG|SHA|ASHA|Total Points|% of Player X Points|% of Gretzky Points
J. Kurri | 15 | 14 | 9 | 5 | 2 | 4 | 1 | 3 | 0 | 53 | 61.6 | 25.0
P. Coffey | 6 | 14 | 5 | 7 | 7 | 5 | 0 | 2 | 0 | 46 | 51.7 | 21.7
G. Anderson | 9 | 14 | 8 | 6 | 3 | 6 | 0 | 0 | 0 | 46 | 43.8 | 21.7
D. Lumley | 13 | 12 | 6 | 2 | 3 | 2 | 1 | 1 | 0 | 40 | 54.1 | 18.9
R. Siltanen | 1 | 4 | 4 | 4 | 7 | 9 | 0 | 0 | 0 | 29 | 46.0 | 13.7
M. Messier | 6 | 6 | 4 | 7 | 1 | 1 | 0 | 0 | 0 | 25 | 28.4 | 11.8
P. Hughes | 5 | 2 | 4 | 2 | 2 | 0 | 0 | 0 | 0 | 15 | 32.6 | 7.08
D. Hunter | 7 | 1 | 5 | 0 | 0 | 1 | 0 | 0 | 0 | 14 | 36.8 | 6.60
D. Semenko | 4 | 3 | 2 | 3 | 2 | 0 | 0 | 0 | 0 | 14 | 58.3 | 6.60
B. Callighen | 2 | 7 | 3 | 1 | 0 | 0 | 0 | 0 | 0 | 13 | 48.1 | 6.13
D. Hicks | 1 | 5 | 3 | 1 | 2 | 0 | 0 | 0 | 0 | 12 | 52.2 | 5.66
K. Lowe | 2 | 2 | 2 | 1 | 2 | 2 | 0 | 0 | 0 | 11 | 27.5 | 5.19
L. Fogolin | 2 | 5 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 10 | 34.5 | 4.72
C. Huddy | 2 | 3 | 1 | 0 | 1 | 1 | 0 | 2 | 0 | 10 | 66.7 | 4.72
G. Lariviere | 1 | 5 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 9 | 40.9 | 4.25
Unassisted | 5 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 6 | 2.83 | 2.83
M. Hagman | 0 | 1 | 0 | 2 | 1 | 3 | 0 | 0 | 0 | 6 | 10.2 | 2.83
G. Unger | 0 | 2 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 50.0 | 1.42
G. Fuhr | 0 | 1 | 0 | 0 | 0 | 2 | 0 | 0 | 0 | 3 | 50.0 | 1.42
K. Berry | 0 | 0 | 2 | 0 | 0 | 1 | 0 | 0 | 0 | 3 | 60.0 | 1.42
M. Forbes | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 25.0 | 0.943
S. Weir | 0 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 12.5 | 0.943
As I remember, Lumley was put on Gretzky's line for the majority of his 50 in 39 run as you said, but for some reason, he was taken off Gretzky's line at around the 3/4 mark of the season.