MTH long ago back in 2004 - had color photos of the R-33 and R-36 Work cars in the Redbird scheme with the yellow ends and black stripes when we were working on the NYC Subway sets and planning for models of various work-rider and work cars. I recall that a number of the real MTA Redbirds (some surplus cars in 2003) started getting that new work car paint scheme treatment back in 2003 at Coney Island Shops. It was easier and cheaper than re-painting the whole car body yellow.
However, THE R-21 CLASS CARS WERE NEVER PAINTED IN REDBIRD COLORS in system service --- NOR DID THE R-21 CARS HAVE THAT 2003 year generated "Redbird Work Paint with Yellow Ends and Black Stripes" Scheme !!! Any R-21 assigned work cars were all painted in the all-yellow scheme with black stripes on the ends long before 2003 !.
You in fact copied the MTA 2003 year instituted " transition work colors " when you 5 years later in 2008 re-painted the ends of your MTH Redbird scheme R-21 cars to create your Redbird color "work car" models, (which you did an EXCELLENT Job re-painting the ends !) , and doing so FOUR years AFTER MTH was already provided with copies of - and aware of in 2004 - COLOR PHOTOS OF NEWLY PAINTED R-33 & R-36 WF Picture Window "Redbird Scheme with Yellow ends, Black stripes" work cars in their files. It is those file photos from 2004 that MTH likely used for these current 2016---2017 production "Redbird Paint" work cars with yellow ends and black stripes !! See photos attached below;