Cars formerly numbered 1010, 1011 and 1044, 1045 now 8000, 8003 got their new numbers back in the late 1980s when WMATA moved its revenue processing facility from the Jackson Graham Building to Alexandra Yard.
What I have always thought was odd was how the Breda cars were numbered, the 2k cars were, base contract 76 cars, 3k cars, option 1 290 cars, 4k cars, option 2 100 cars.
As built the only difference between the 3 orders is the 2 and 3k cars had DC cam control propulsion systems in them them, the 4k cars had DC chopper propulsion systems in them.
All of them could have been numbered within the 2k series, Base order, 2000 - 2075, option 1, 2076 - 2465, option 2 2500 - 2599 to differentiate them from the DC cam control cars.
WMATA could have numbered them from 1500 up Base order and option 1, 1500 - 1865, option 2 1900 -1999 to differentiate them from the DC cam control cars. This numbering schema would have allowed both the CAF and Alsom cars to be numbered in the 2000 and 2500 series respectively leaving 3000 up for the Kawasaki cars.
By the time WMATA started using the 5ks numbers, the 1ks numbers would have become available as the result of retirement.
If a heritage fleet were established the numbering schema to differentiate them from the revenue could be done by prefixing their original numbers with an H or 0.
I will note, the Rhor cars were a single order for 300 cars and 1 unfitted out car body.
John in the sand box of Maryland's eastern shore.