In short, without a Date Code we can never be certain.
Although there are no Date Codes, the Serial Numbers are consecutive,
from the earliest Model 2 right up until the last Model 6.
So estimates can be made (Guessed).
Based on what we know, the best estimate is as described on Post # 2570
https://www.vintage-radio.net/forum/...=4343&page=129
From a Historic point of view, 1927 is probably the only Date of importance
for the series 1 Model 2 and 1930 for the second series.
Ian