I used a Canonet 28 (bought cheaply without a manual) in 1990's with a SR44 battery and soon discovered serious under exposure. Well - I thought - the meter has seen better days and compensated using a setting "ASA 25" for ASA 400 film if my memory serves me right. Worked well enough for negative films.
So this puzzle is settled then. The thing might still work properly - there was nothing wrong with the picture quality.