Got some good info from ‘Hari317’ on the WUS forum. Here’s what he told me:

‘Little information is available about their early models so we dont know if your watch predates the name watches or not. Citizen is translated into Hindi as “Janata” and the Janata is still their bread-butter model. ‘

And this is particularly useful:

‘The case back consists of three segments: factory code, case code and case producer code. I don’t have sufficient documents with me to exactly decipher the codes. however, the first field on your case back is 01 which indicates WF-1 at Bangalore.’

So I can forget trying to date mine from the number on the case back:

Hari317 also provide this link to the HMT website, which gives info on the first factories in India etc.:

History | HMT Watches

Thanks  again to Hari317 for his help 🙂  Finally, here’s a closer pic of mine: