Its actually better than that.
All 3SUBs and 2NOLs were converted from older LH stock and LBSCR OH units, dating back to the 1890's even to the point that a few 4 wheel coach bodies were paired up on new underframes
Then all of these units were rebodied into Class 405,415,416 and the EE507 motors rewound for higher power.
Then when they were withdrawn their motors and equipment was reused on the class 455/456s.
So, EE507 motors on Class 455s were on 4SUBs ex 3SUBs from as early as the 1920's
They are hence the opposite to this threads point.
Not all 3SUBs - the first 138 (Nos 1201-1310, 1496-1524) were built new to provide a pool so that Loco-hauled stock could start to be converted.
The rebuilding of steam stock often used parts of three different bodies. (David Brown's comprehensive history of the SR EMUs gives the details)
Of the 486 trailers built for 4SUBs, either in all-new units or for augmentation of older 3SUBs, (Nos 10121-10400, 10419-10481, 8901 - 9034), I can find only about a dozen that were withdrawn before 1972. Over 400 were converted for use in 4EPBs, mostly in the 1950s but some as late as 1983 (matched with ex 2HAP motor coaches)
As has been noted, some of these trailers were new bodies on underframes that had previously carried bodies converted from loco-hauled stock. So veritable hundred-year old "Trigger's Broom"s - two bodies, two underframes, and three sets of traction equipment (including steam haulage).
Many of the earlier augmentation trailers, as well as the first ten 4SUBs (the "Sheba"'s) were not actually all-steel as they had wood-and-canvas roofs. According to Hugh Longworth's listings, the first truly all-steel trailer was No 10391, built in 1946.