Lately I have seen many problems arose when collectors saw a Bi-lingual Shanghai with a different year plug.
They described it as a mystery cancel, someone suggest that is just the time of the day and others sub-offices. If you haven't seen one yet, below is an example with a postcard used in 1904 and the Shanghai Bi-lingual instead of '04', is a '20'?

I have in my collections a few other curious examples of such cancellations, most of them are rather blurred but they show instead of the right years, '25', '26' etc. I am not suggesting that because of a number larger than '24' that it must be a Sub-Office cancel. I have no definite prove that it is either of the two, it might be that some are Sub-offices and others are Dispatch time??? Do anyone have a Post Office record of Shanghai at the time? If you do, please drop me a line.
The following are example of '25' & '26' on bi-lingual Shanghai cancel.
This cover send from Wuhu to Shanghai in 1913 have a bi-lingual Shanghai with a '25' (see insert).

This next example is a cover I have under the Tombstone cancellation page. It was send in 1906 and it have a Shanghai bi-lingual of '26' (see insert).

Please note that none of the cancellations on the above covers had been re-touched or modified.
Anyone have a better suggestion? What else could it be? Please e-mail me.
Thank you.