Looks like the Lucasarts game came out in 2003, while the D-Day P-38 was released in 2001-2002, so they could have copied it...
The S1 P-38 is an actual P-38, save that 21c had to perform a few edits to the nose art to please the PC crowds. The actual plane was called "Les Femme, Les Vin, et les Chanson" (French for "Wine Women & Song") featured prominent nose art with a naked lady in a martini glass, and had swastika kill markings. Not quite the things I'm sure a parent would have liked to have found on the model plane they got for little Johnny at Toys R Us
Jackson at one time made the historically-correct decals for the S1 P-38.
To date, there have been 8 21c/JSI P-38s:
S1 Wine Women & Song
S2 Samantha Peyton (fictitious scheme)
S3 Putt Putt Maru
S4 Louise/Sharkmouth
S5 Haleakala II
S6 Pudgy V
S7 California Cutie
S8 JSI repaint of Putt Putt Maru