Here's my guesswork...
1954 Original model launched with 5' BC holders, 2' and 4' models came later with bipin 'tombstone' lampholders and matching endcaps? Were there 3' and 8' versions? What attachments were available? Not seen a twin version!
1960-69 replaced by Atlas (also branded Ekco) Superslim in 2', 4', 5' and 8' (not sure if there was a 6' then) Single and twin, with quickstart options, 5' 65w followed in later models. Opal diffusers, trough refelctors and louvres that clipped onto the tube in 1' sections available have been seen on these fittings!
1970-75 Grey Atlas (and a few Ekco and even Mazda!) Pop Pack launched, 6' available,
1975-81 As above in white branded Thorn without recessed logo on side. New
1993 onwards. All went downhill from here!